FAQ: New answers

SuperMemo on CD-ROM
(Robert P. Miller, , Oct 03, 2009, 22:48:06)
Question:
I am interested in purchasing the latest version of Supermemo for Windows (Vista, Windows 7, etc). However, I would prefer a CD-ROM rather than downloading the software. Could I receive a copy via conventional mail?
Answer:
As of SuperMemo 2000, we no longer release standalone SuperMemos on CDs/DVDs. The reasons are as follows:

How can I review my material on the same day I add it to SuperMemo?
(NamJongmin, , Monday, October 12, 2009 2:35 PM)
Question:
Why is that I can't review the material right away, but have to wait a couple of days. I know that's to achieve the benefit of spacing effect. Yet, is there a way to review the material right away?
Answer:
We do not review the material on the same day because of the spacing effect that will make the review ineffective or even counterproductive. We also do not do it to have more time for learning new material, or for doing other things. If you add learning material to SuperMemo today, and you do it with deliberation, reviewing it right away is tantamount to cramming, and you should restort to it only in emergencies (e.g. if your exam comes tomorrow). To review your new items on the next day, open the item set in the browser and choose Review All. To review your items yet today, choose Random Test instead. Note that Random Test will leave no trace of the review in your learning process. This means that SuperMemo will not take a correction for whatever memory effect you will manage to produce with instant review.

Solutions for people suffering from DSPS
(Aaron Burtle, , Oct 01, 2009, 23:36:26)
Question:
I recently came across your write up regarding polyphasic sleep. The idea of sleeping in naps spread throughout the day intrigued me, as I have always suffered from what I was unable to properly quantify, but now know is DSPS. If I do not use an alarm clock, and go to sleep when I become tired, I see my sleep/wake times shift to significantly later times every day (hours later). This has been a constant source of frustration for me, and I considered a polyphasic schedule in order to help correct the problem. However, after reading "polyphasic sleep: facts and myths", I have decided this would be a sincere waste of my time. I was wondering if you had any experience with helping those who have DSPS maintain a more, "normal" schedule. Is a bi-phasic sleep schedule more suitable for someone with this sleeping disorder (sleeping from 2-7am with a nap from 1-2pm for example)? Google has told me that the most common treatments seem to be rotating ones sleep until they line up with civilized society and then using something like bright light therapy to keep the clock reset. Will this be treating the symptoms alone or actually getting at the root problem? Do you know of any other techniques which could help me situation?
Answer:
Probably, most of the cases of DSPS can be explained by a lack of compatibility between the genetically determined sleep regulatory system, and the lifestyle. You can easily cure the disorder if you decide to change your lifestyle. However, such a change is usually not feasible due to the type of employment or family life conditions. This means that you are probably, for a while, sentenced to a constant battle with your body clock.

It is true that the best known remedy is to cycle to alignment and reset the cycle. In other words, if possible, use your natural tendency to go to sleep 1-2 hours later, until you align with the desired sleep rhythm. At that point, your battle begins by efforts to provide strong morning resetting stimuli (e.g. bright light, stress, exhausting exercise, etc.). Those can be enhanced by evening measures such as melatonin or the avoidance of light, stimulation, stress, etc. In other words, you need to provide resetting stimuli in the morning, and avoid evening sleep delay factors such as computers, TV, artificial lighting, etc. For most people, a degree of sleep deprivation is more acceptable, than several futile inactive hours in the evening in a dark room.

Using a biphasic sleep like you describe (2-7 am, 1-2pm) is a good idea. However, you must be aware than naps taken too late are likely to delay the sleep phase making matters worse (even though the same naps can be a blessing for your mental performance, alertness and creativity).

Needless to say, polyphasic sleep does not bring any advantage to a DSPS person. In DSPS, you suffer because of a slight misalignment of your main circadian low. Polyphasic sleep disregards the circadian cycle entirely making matters worse. Ad hoc napping (as opposed to planned/artificial "Uberman" napping) is a reasonable way to alleviate sleep deprivation, however, (1) it needs to follow your natural brain needs, (2) it may have a detrimental impact on the cycle itself (often worsening the degree of DSPS).

In conclusion, DSPS epidemic can be considered a civilizational disorder in which the pressure of a modern lifestyle stands in disagreement with millions of years of evolution. In the long run, once we fully understand all biochemical and hormonal processes underlying sleep, it is possible that mild pharmacological intervention will make it possible to regulate the circadian cycle. Currently, this is possible to a degree, but you are bound to experience side effects and research on the matter is still scant.

You can upgrade without having an older SuperMemo installed
(Vince Mooney, , Thursday, October 15, 2009 2:45 AM)
Question:
I purchased SuperMemo in around 2004 and operated it on my previous laptop. I would like to upgrade to SuperMemo 2008 but load it onto my new laptop. Is this possible? Can I order the upgrade onto my new laptop even though the program does not already exist on that computer?
Answer:
Yes. You can upgrade to SuperMemo 2008 and install it on your new laptop. You do not need the previous installation. Upgrade verification occurs at the time of ordering on the basis of your previous data. If you data has changed, please get in touch via e-mail to have it corrected.

An expert on TV said clearly that we get lowest alertness at 8 am, and then in progressively increases. This is opposite to what you claim!
(anonymous, , Oct 20, 2009, 10:15:29)
Question:
An expert on TV said clearly that we get lowest alertness at 8 am, and then in progressively increases. This is opposite to what you claim!
Answer:
Lowest alertness at 8 am might be true for people who go to sleep too late and wake up with an alarm clock. However, it is definitely not true in free running sleep. The person who got lowest alertness at 8 am would most likely keep sleeping till 10-11 am and only then wake up naturally. If you use SuperMemo and collect your sleep data, you can see clearly on your alertness graph, that alertness is highest at the beginning of the day (perhaps starting with the first our after awakening due to the transition from sleep to wake that sometimes may take some time). Low morning alertness can only be explained by the misaligned circadian rhythm. If circadian lows occurred earlier, morning would be brisk and alert. In other words, the expert might be right. Most people wake up too early and are sleepy throughout the morning. But this is a situation we should all strive to eliminate by getting sufficient sleep and sleeping in the optimum hours.

I am getting asked about the password again and again
(Abrahams, Israel, , Thursday, October 22, 2009 9:35)
Question:
Every time I open supermemo it asks me for the unlocking password which you gave me. How do I get it to stop?
Answer:
Once you insert the password, you should never be asked to insert it again. The password is stored in your learning material. This means that you need to preserve your learning material for use. One of errors users make is to install SuperMemo in temporary folders or running it directly from inside of a zip file. In such cases, you may always create new files on startup without ever having them stored properly on your disk. Be sure you run SuperMemo from a clean own folder that allows of read-write access. Learning material path and SuperMemo path can be displayed in File : Properties (you may need to change File : Level to see this option).

Every operation in incremental reading should leave a trace in your memory
(marjur, , Thursday, October 15, 2009 16:25)
Question:
I plan to start the learning process late at night. The topics and items are mixed. However, I prefer to leave the topics for the end of my learning session, so whenever I get a topic, I execute "Learning->Later today". When I finish with the items, I start working with the topics. But I suddenly may feel tired and decide to go to sleep. What am I supposed to do with such untouched topics? Shall I just leave them untouched? (in that case, will they be automatically rescheduled by SuperMemo) Or maybe I have to manually reschedule them before I close SuperMemo? Or should I quickly display each of them and execute "Learning->Execute repetition" (btw: when do you recommend using "Learning->Execute repetition")
Answer:

You should always keep in mind two essential rules of incremental reading: Every incremental operation should leave a trace in your memory. One operation on a piece of data is better than two operations at the same time. Those rules will immediately produce the answer to your question. If you have unprocessed topics in the queue, leave them to SuperMemo. Let auto-postpone and auto-sort do the work for you. One of the greatest offences incremental readers commit is to do processing operations without actually learning anything. For example, when a topic arrives, and you take a little peek, you may think: I do not like this one. Let's do it tomorrow. Or I am too sleepy for this one. Or this one will take too much time. If you find yourself in a loop and constantly rescheduling the same topic, or spending time rescheduling a number of topics, you are hurting the efficiency of learning! This is the time that could be spent on more productive steps. If you do not like a topic, you can deprioritize it, or schedule it at a remote date once. Otherwise, you should do something. Anything that will bring you closer to either processing the topic or deleting it altogether. You could just read the first sentence and decide how to process it. If you then Execute Repetition, you will at least be one step closer to having that topic processed or eliminated.

Why does not SuperMemo experiment with shorter intervals?
(Jeremias Sauceda, , Tuesday, November 10, 2009 9:14)
Question:
I have been using SuperMemo to learn Japanese, it's been great! I have also used it to teach my children math and they enjoy it very much. When I started learning Japanese I used the Pimsleur tapes which use very short intervals during each lesson; 5 seconds, 25 seconds, 2 minutes, 10 minutes, etc. according to Wikipedia. Also Anki reviews missed repetitions after 20 minutes. I am curious if there is a reason SuperMemo does not use a similar approach for learning new material or dealing with the drill queue? Or is it just a feature you have not explored at this time?
Answer:

This is one of the most frequently questions about the SuperMemo method. SuperMemo is all about the maximum speed of learning understood as the increase in the total body of knowledge. Repetitions at intervals shorter than those computed by SuperMemo are sometimes referred to as microspacing. Those repetitions may operate on short-term memory (in intervals of minutes or hours), or on long-term memory with a strong impact of the spacing effect. As such, those repetitions are of far less value than the usual repetitions served by SuperMemo. If you learn for an exam, or strive at high fluency or speed of recall, microspacing may play its role. However, if you work on long-term memories that are to last for years, those additional repetitions are either of lesser value per memory effect, or even counterproductive (i.e. not only reducing the inflow of new knowledge, but also adding extra work to retaining the equivalent body of material). Boosting short-term memory with microspacing has a negligible long-term effect (esp. for long-interval repetitions). Any attempt at repetition ahead of time inevitably evokes the spacing effect and thus reduces the impact of the repetition (even though many users just cannot resist the temptation and abuse the tools for early repetitions provided by SuperMemo). The value of microspacing cannot be demonstrated with SuperMemo, or with memory models used in SuperMemo, nor with any notable research in the field of spaced repetition (if you happen to encounter sources claiming otherwise, please get in touch).

Classical SuperMemo adds a concept of the final drill, which also can be considered a form of microspacing. Final drill might be useful if you work on high volume of high interference memories (e.g. vocabulary of a foreign language). Its main role, however, should not be as a reinforcer of memories, but as a tool to establish or re-establish memories in cases of poor recall. In other words, final drill is not to be used for microspacing, but to build the first imprint of memories that one failed to imprint at the first attempt. As compared with standard repetitions, final drill can also produce less value per time, and it is recommended for advanced user to never use the final drill. The most efficient approach is to develop a habit of never passing a failed grade repetition without an attempt to establish some form of a correct memory imprint. This may be difficult for beginners. But this habit can be developed overtime, and an advanced student should never need to use the final drill. If you learn a foreign language, you may still want to use the final drill as a form of battle against memory interference. However, if you use incremental reading to gain structured knowledge (e.g. of sciences), going through the final drill will only add to your learning time. If you feel you still need the final drill in incremental reading, look closely at the quality of the learning material and your repetition habits, esp. the ability to focus on each and every repetition.

All the claims above are not to say that Pimsleur and/or Anki take a wrong approach. Each method and application have their own focus, goals and usership. If you learn high-interference knowledge (e.g. vocabulary), or add a degree of procedural learning (e.g. pronunciation), or add a degree of pattern recognition (e.g. comprehension), or limit the size of the body of knowledge (e.g. core vocabulary), optimum strategies will change. Experimenting with different approaches can serve as a rich cross-fertilization for the future (as evidenced by your interesting question). Moreover, SuperMemo works on the assumption that the user is aware of the optimum learning techniques. However, there are psychological effects related to concepts such as the final drill, or microspacing. If the user experiences a false sense of higher productivity, or just plain enjoyment, the benefits may outweigh the costs. This is why having many systems with many approaches allows of richer comparisons that are not just limited to dry theory.

OF matrix is 20x20
(saeideh monfared, Iran , Nov 07, 2009, 14:34:41)
Question:
How big is the OF matrix used by SuperMemo (what are its dimensions)? Is it the same for SuperMemo 5 as it is for SuperMemo 2008?
Answer:
The matrix has 20 rows and 20 columns. It can be inspected in SuperMemo 2008 with Tools : Statistics : Analysis : Matrices : OF Matrix. It is the same matrix as used in SuperMemo 5, however, its entries are processed differently in successive algorithms. The 20 rows correspond to 20 repetitions (or repetition categories in later SuperMemos). The 20 colums correspond to A-Factors in newer SuperMemos (or E-Factors in older SuperMemos). The entries of the matrix determine the intervals between repetitions. Each item difficulty (A-Factor or E-factor) has a different set of intervals for different repetitions (or repetition categories).

You can edit references in the reference field
(marjur, Poland , Oct 31, 2009, 01:06:20)
Question:
Is it possible to edit references once I have them in elements, e.g. delete some parts? If so, how (directly in elements or perhaps in the registry)? Most of my references have this format:
#Title
#Author
#Date
#Source
#Link
#Article
#Category
I just wanted to leave #Title, #Author, #Date, #Source, and delete the rest. I'm not sure if it's safe and I don't want to ruin my collection. On your website you wrote something like this: "Important! Do not add texts below references. All reference field area is owned by SuperMemo. Any modifications to that area will be treated as changes to reference fields. Illegal changes will be discarded without warning." What are "illegal changes"? Given this information, I'm not sure if the program will accept reference changes at all
Answer:
You can edit references in the reference area (which is pink by default). You can safely delete reference fields, but you need to decide if that change should be local (for that element only) or global (for all elements using this reference). You will not be able to delete #Article or #Category fields because they are added automatically to references (not being a part of reference). You can freely change the text of references. Illegal changes are all changes that do not comply with the reference format, e.g. lines that do not start with reference field tags, or lines that start with unknown reference field tags (e.g. #Country). If you are unsure how this process works, import a single article from Wikipedia to a newly created collection, create some extracts and play with editing to see how references are processed.

Should items be converted to plain text in the end?
(marjur, Oct 29, 2009, 20:51:00)
Question:
Once fully processed, do you recommend changing ready items from HTML into plain text?
Answer:
Plain text takes much less space. Your collections will be faster to back up. All you need to make sure is that HTML does not contain information that may be needed to effectively remember the item (e.g. is the context fully retained once references are removed)? In the long run, simple plain text items might do their work better by depriving you of additional cues as to the correct answer. However, you will always get the best answer to your question by simply experimenting on your material. Leave some of your items as HTML and convert some to plain text. After some time you will probably have your own conclusions and preferences.

All activities included in the schedule are added to the statistics.
(M.M., Nov 19, 2009, 01:31:26)
Question:
I am using Plan to compile my learning time statistics. Why are unmarked/unchecked activities such as Reading included/counted in my 2009 Year Total?
Answer:
All activities listed in the schedule are taken into consideration. SuperMemo has no way of knowing if you used Begin to mark the beginning of each activity and set up the alarm, or simply stuck to the plan religiously and completed it without using Begin. To simplify things, SuperMemo adds all activities from the schedule at the moment when you choose to save the statistics. All activities have their duration taken from the ActLen (actual length) column. The only exception are activities skipped and activities with a manual expression of the duration (e.g. ++Reading 22). If you do not want an activity included in the statistic, simply delete it.

What if I reinstall my operating system?
(Marcin Ostrouch, Monday, November 09, 2009 1:33 PM)
Question:
I'm bound to reinstall my operating system before very long. I understand that I will be able to install SM2008 then withouth any problem (i.e. download whatever the sm08inst.exe needs to download). Is that so?
Answer:
If you reinstall Windows on the same computer without formatting the hard disk, SuperMemo 2008 should work without reinstallation (some older versions may need to be moved away from \Program Files). If you reinstall Windows and clean up your hard disk, you can move sm08inst.exe to any folder and reinstall SuperMemo 2008 (you need to have access to the Internet). If you reinstall Windows, and do not have any backup files, you can write to us. Your download instructions will be resent. If you write from a new e-mail address, you may need to identify your original order (e.g. by name, address, order number, etc.).

After repetition, SuperMemo modifies OF matrix entry that was used in computing the interval
(saeideh monfared, Nov 19, 2009, 23:17:02)
Question:
I Supermemo 5 algorithm which is explained here: http://www.supermemo.com/english/ol/sm5.htm in step 7: what do you mean by relevant entry of the OF matrix?
Answer:
SuperMemo uses a simple principle: "use, verify and correct". After a repetition, new interval is computed with the help of the OF matrix. The "relevant entry" to compute the interval depends on the repetition (category) and item difficulty. After the interval elapses, SuperMemo calls for the next repetition. The grade is used to tell SuperMemo how well the interval "performed". If the grade is low, we have reasons to believe that the interval is too long and the OF matrix entry is too high. In such cases, we reduce the OF entry slightly. The "relevant entry" here is the one that was used previously in computing the interval (i.e. before the interval started). In other words, in both cases, the "relevant entry" is the entry that is used to compute the interval (after n-th repetition) and then to correct the OF matrix (after the n+1 repetition).

Where is the download button
(John Hansen, Wednesday, November 11, 2009 12:40 PM)
Question:
I'm sorry but I can't find the download button on your webpage to download supermemo. Be advised I am currently in China and maybe it has to do with their firewall or something. Not all web stuff seems to work reliably over here
Answer:
If you fail to download during the purchase, you can always receive download instructions later via e-mail (use the confirmation of your order to get in touch). You can also find various emergency instructions here: http://www.supermemo.com/help/faq/shop.htm (incl. how to redownload). Note that for unclear reasons, Yahoo opted to place the Download button in the middle of the page, while most customers tend to look for it at the bottom of the page. The button isn't too big either. This is why it is not unusual to miss this button even if the page loaded correctly.

Changing the OF matrix in SuperMemo
(saeideh monfared, Nov 19, 2009, 23:17:02)
Question:
Would you please give me an OF matrix sample and explain how it will be changing, and why we need to create this matrix fully at first?
Answer:
You can see the OF matrix in SuperMemo in Tools : Statistics : Analysis : Matrices : OF Matrix. This matrix changes in time to make sure that the intervals produced meet the optimization criteria (in the latest SuperMemos, the only criterion is the requested forgetting index). We set the original value of the matrix to be sure we can use it in computing initial intervals that will later be used in verifying and modifying the matrix. The initial value of the matrix is taken from earlier versions of SuperMemo. In the late 1980s, some experiments were made to prove that this matrix can easily be produced within a couple of months from a constant matrix composed of all entries equal to 1.5, 2.0, 3.0 or similar using early SuperMemo algorithms (e.g. Algorithm SM-5).

How to deal with material overload in medical school?
(clarence166, Friday, November 27, 2009 14:57)
Question:
How do you deal with your repetitions if the number is so many that you can't add new material because of the time the repetitions consume? About two weeks ago, I started incremental reading on a textbook of anatomy for an exam (medical school). The exam was done yesterday. Because of incremental reading, there are ~4100 elements in my collection shown in the statistics window. 70% are items, 30% are topics. Currently, my daily number of repetitions is around 400-500, half of which are items and half of which are topics. It seems to me that I don't have the option to slow down on adding elements to SuperMemo. There will be another exam in two weeks time again. If I gradually add another 4000 elements for the next exam, I might not be able to sleep due to the number of repetitions. According to the Workload shown by SuperMemo, the number of repetitions will only be below 100 (items+topics) after a week. Will you only do repetitions as time allows?
Answer:
You have just proved again that the demands of a medical school go well beyond the human capacity to learn. That's a norm for most school. Even SuperMemo is powerless here. With this realization you need to adjust your strategy accordingly. Your overall strategy could look as follows:

How does incremental video work?
(Krzysztof, Dec 10, 2009, 19:56:25)
Question:
How does Incremental Video work in SuperMemo 2008? Do you chop the film and piece it at intervals to the user?
Answer:
In incremental video, it is the user who decides which portions of a video are important to remember. Those portions are part of a standard learning process known from other applications of SuperMemo. Each portion of the video forms a separate topic that is reviewed at increasing intervals.

Medical knowledge: too much!
(German Salazar Pareja, Dec 29, 2009)
Question:
You write that "the demands of a medical school go well beyond the human capacity to learn. That's a norm for most schools. Even SuperMemo is powerless here". This is a fallacy, more than one million physicians in the world are your proof. Human capacity to learn is huge. Not infinite, but huge. I don't have the numbers about this capacity, but I could search it if necessary. However, I've also struggled during my med school years, probably because I was concerned with learning the most I could. I believe medical school curricula is designed with other purposes in mind, trough you career you'll always have time constrains, the ones who survive this selective process are not only those who study most, but those who learn how to deal the the problem of time constraints and still can do the most of the learning in med school
Answer:
You need to interpret the quoted sentence in the context of SuperMemo. Basically, in the context of SuperMemo, cramming is not considered a form of learning. Consequently, the capacity to learn, should be understood as the lifetime capacity of the long-term memory storage rather than the ability to store a large volume of information in memory in a short period of time (e.g. before an exam). Similarly, demands of a medical school, should be interpreted as the student-perceived demands on what material is absolutely necessary to know. Those demands are quite different from what material is actually known at graduation (let alone a few years after the graduation). Using this interpretation, if you raise the bar for what you consider "learned", and raise the bar for what you think you need to know, you arrive at the point where it is not possible to learn all that you think you should know as a medical graduate. There are indeed millions of active physicians today, however, each would fail some basic medical knowlege questions when tested today. This is not to say that all physicials are bad physicians. This is only to say that each and every human being, however smart, has his or her own patches of ignorance, even within his or her own field of expertise.

Two methods can be used to easily illustrate how university knowledge exceeds human capacity to learn:

Comparing SuperMemo on paper with freeware applications
(Dan S.K., Russian Federation, Dec 28, 2009, 10:03:32)
Question:
Is figure 2 table from http://www.supermemo.com/articles/paper.htm applicable for words cramming? Paper-and-pencil SuperMemo article is soon 20 years old and I believe you have more accurate data on time spacing when it comes to using no algorithms and computers, but just constant schedules. I also came across this http://www.learnwords.ru/repeat.html. And it is stated here that:
1st repetition should be scheduled 30 minutes after reading words for the first time
2 - after an hour
3 - after 9 hours
4 - after 24 hours
5- after 3 days
6- after 6 days
7- after 12 days
Answer:

The term optimum interval used by SuperMemo is misleading and inaccurate as optimum intervals do not exist until you define the criteria for computing the optimality. SuperMemo uses the concept of the forgetting index to define the optimum interval for a given desired retention level. SuperMemo on paper was defined in 1985 and roughly approximates optimum intervals for heterogeneous material based on the minimum information principle and the forgetting index of 10%. This definition strongly depends on how heterogeneous material is defined as distribution of material difficulty can dramatically impact the value of intervals. The original definition of SuperMemo was based on the material largely composed of word pairs and should be applicable to most selections of foreign vocabulary material within the same language family. This means that it could work nice for Poles who learn English, but might need some revision for Swedes who learn Russian, and a major revision for Spaniards who learn Korean. Naturally, all those theoretical divagations are of little relevance today when we can employ computers to compute the optimum spacing of repetitions for all individual pieces of information.

As for the quoted Russian software for learning words, it seems to approximate SuperMemo with an extra criterion of adding a bit of "mental comfort". It takes intervals used by SuperMemo on papers (some shortened by a day), and adds four extra microspaced repetitions before the first repetition that would normally be scheduled by SuperMemo. This resolves the problem of mental discomfort experienced by those who encounter SuperMemo for the first time where the first repetition is often scheduled at a far later time than expected by the user. A frequent complaint from beginners is "why are intervals in SuperMemo so long? by the time I review, I no longer remember". Microspacing has been proposed over and over again from various quarters (incl. more advanced users who believe in theories that back the value of microspacing beyond the simple extra added mental comfort).

The benefit of spaced repetition as compared to traditional learning is substantial enough to make the above differences of less significance. You can use SuperMemo on paper, simple freeware applications or the newest SuperMemo algorithms. These all are likely to be highly beneficial.

Incremental Audio
(ernesto.bergeron, Mar 10, 2010, 04:24:51)
Question:
Your system of incremental reading is truly efficient. Have you thought about incremental audio? Imagine a person hearing a poem one phrase at a time, with cloze deletions, and repeating overtime. Does it work under the same principles as incremental video or incremental reading?
Answer:
Incremental video can serve as incremental audio. Currently you cannot "cloze delete" portions of the video, however, you can, with some effort, use video extracts as answers to text questions, or even video questions. Incremental video is currently most suited for processing video or audio material passively with the most interesting portions extracted for passive review as topics. In the future, indeed, incremental video should support "cloze deleting" portions of video to meet the functions you envisage.

Writing my own SuperMemo
(Greg Szczotka, Jun 15, 2010, 14:11:02)
Question:
I am trying to write a online learning system in php based on your algorithm. Does the article http://www.supermemo.com/english/algsm11.htm contain everything what's needed to write it in php? Or are some parts of algorithm not published? Which version of algorithm do you recommend? I know a lot of software use version 2 but I'd like to use the best one.
Answer:
The description of the algorithm may be helpful in writing your own spaced repetition system. You can follow those guidelines closely or use similar optimization methods, or just use it as an inspiration for an entirely different approach (e.g. hill climbing, neural networks, memory models, fuzzy logic, and more etc.). Rather than reading the most recent description, you could benefit more from reading the history of SuperMemo algorithms detailed at supermemo.com, which provide a better illustration of general assumptions behind SuperMemo. That includes the earliest algorithm for use with computers used in SuperMemo 1 and SuperMemo 2. The newest algorithm is pretty complex and you might go that far once your system is operational and successful. However, to employ the newest version, you would need to get in touch with SuperMemo World to obtain a license. In the meantime, you could use simpler versions to give your system a try run.

SuperMemo 2002 not compatible with Windows 7?
(G.K. Shaenan, Wednesday, July 21, 2010 5:05 AM)
Question:
I just bought the SM 2002 and a few other things, and I am getting an error message that it is incompatible with Windows 7. Is that true or do you have a fix?
Answer:
The old installer that comes with SuperMemo 2002 no longer works in new Windows. If you have Windows 7, please write to receive alternative download & installation instructions.

SuperMemo can always be purchased in any country
(anonymous, Aug 08, 2010, 08:15:16)
Question:
Will SuperMemo Store (super-memo.com) block orders from my country once I become a successful franchisee?
Answer:
No. You will need to ensure that users that come to your native site, stay in your site. Blocking orders coming from specific IPs can be circumvented via VPNs. When done for marketing reasons, such blocks often results in absurd situations. For example, you cannot order downloads from the Microsoft Store if you are located in one country, but you can easily do it from a neighboring country (even within the European Union). Those customers are often sent to purchase shrink-wrapped products from a local dealer, often at higher prices. That's a global waste of time, resources and energy (both physical and human). We want to see SuperMemo always available via simple downloads from any country on the globe: free or commercial. Some download problems may be a result of a local government policy (e.g. from China).

Are Categories treated distinctively in learning?
(anonymous, Jul 22, 2010, 16:10:40)
Question:
I was wondering if Categories are treated differently concerning the scheduling of the items, since different subjects hold different levels of difficulty.
Answer:
Items belonging to different categories are treated in the same way. The only difference is that you can define a default forgetting index for the entire category. New items added to a modified category will have a distinctive forgetting index. This way they can be reviewed more often, or less often, and they can be remembered better, or worse, depending on the setting.

How is the RF matrix computed?
(Edward Douglas, Jul 31, 2010, 21:19:41)
Question:
I have not managed to find information on the functions of approximating the RF-matrix in SuperMemo
Answer:
The RF-matrix contains actual data/measurements, and thus is not an approximation. Naturally, this data can be considered the approximation of how your memory works: the more data you get, the closer you get to the real reflection of your memory. In simplest terms, RF matrix contains columns that reflect item difficulty, and rows that reflect the strenght of memory. For each entry SuperMemo collects repetition data and plots a forgetting curve, i.e. how much you forget with the passage of time. Each entry of the RF matrix corresponds with the point in which forgetting reaches the level defined by the forgetting index. This way, if you know how difficult an item is and how well it is remembered at the moment of the repetition (or how many repetitions it went through), we can predict (roughly) at which moment of time the probability of forgetting will equal the forgetting index. That's the time we want to have the next repetition

Current tasklist is marked as deleted
(Eugene Huang, Oct 22, 2010, 16:40:01)
Question:
Current tasklist is marked as deleted Choosing new tasklist: " "
Answer:
This error can occur in any circumstances in which SuperMemo is asked to use a tasklist that has already been deleted. For example, if you manually change the current tasklist in collection.ini file. As this error should not normally occur without unusual actions, it is important to make a backup of the collection and run File : Repair collection. This is to ensure the message is not a result of some more serious error, e.g. caused by a computer crash, etc.

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