So the basic premise is that it would vary the spacing based on how well you remembered the fact. Would start daily, then if you know it well, go weekly, then monthly etc.. The idea is that it's dynamic and mimics your memory decay. Memstash doesn't get feedback from each alert, it just shows you. There is no interaction or feedback to know how well you remembered each item which would then inform the spacing. You can read more here if interested: http://www.supermemo.com/articles/theory.htm