I do work for a lot of groups, often just a few hours a month (if that). I was involcing one of them this week & added three sessions of 3/4 hour, 1 hour & 1.25 hours.... & let them know that they owed me for 2 hours work. They let me know that I'd underbilled by an hour. And I an accountant's daughter! I'm blaming the heat but sheesh!