Hmm not so clear wording there, it means you do reviews twice and count them per day. The result is very spiky (some days lots of reviews, then zero, …). Let’s say you get 0/900/0 reviews in three days. The graph will show 300/300/300 (the corners will be averaged with the things around it, though) instead.
Hmm actually the graph looks better than expected, I remember for maximum reviews it was quite freaky.
