I have been experimenting with spaced repetition algorithms for around two years now, and I've found that for me, an a simple exponent with base of 2.71828 (e)

I have been experimenting with spaced repetition algorithms for around two years now, and I've found that for me, an a simple exponent with base of 2.71828 (e) to be optimal for learning short question/answer pairs. This means, every time I successfully recall the answer to a question, I increase the interval of when I will be challenged with it again by about 2.71828 times since I had seen it previously. This is with a recall failure rate of about 5%, which I'm trying to maintain. (If it's nearing 0, then you're probably wasting time being challenged too frequently.) This is on a data set used daily for 30 minutes, reviewing about 50 older questions and encountering around 3 new ones per day.