# Details about the comparison between SM-17 and SM-2

## Question

In Algorithm SM-17 vs. older SuperMemos, the retrievability prediction in SM-2 can be obtained from:

SM2R:=Exp(-MDC*Int/SM2Int)

But the page didn't provide the value of MDC. Can I use SM2Int as stability? In this case, MDC = -ln(0.9) = 0.1053605157.

I'm building benchmark for spaced repetition algorithm, here is the link of our repo: https://github.com/open-spaced-repetition/fsrs-benchmark

SM-2 is a popular and famous spaced repetition algorithm, so I want to add it into our baseline.

## Answer

In SuperMemo 18 code you have this:

MDC:real; //memory decay constant MDC:=ln(10/9);

The original algorithm is described here. The term stability was not used then, but interval reflects the concept of stability.

(thank you for working on this, independent code will be helpful to verify claims of SuperMemo)