Algorithm SM17. R-metric problem

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From: Raymond
Country: France
Sent: Dec 1, 2017
Subject: R-Metric

Question:

my R-metric is positive, but in my first repetitions (short interval) it always goes negative. only later it improves. Why is it so?

Answer:

First forgetting curve collects all data from all first repetitions. This makes it less flexible. In SuperMemo 8..16, it collected only 255 repetitions per bin (i.e. interval category). If you change the difficulty of your material, SM16 will adapt, SM17 will average old data with new data. This puts it at a disadvantage at a time when the new material flow in (assuming it is much easier or much harder than the average).