I've been playing around with our member/visitor tracking system, thought someone might find this useful. There have been a few posts out there about tracking attendance and assets for different classes, there are some really amazing websites like Open Black Belt, The Dojo Manager and My Attendance Tracker. Sometimes, though, it's more convenient to have it tailored to needs as they change.
I hope this works when it's exported, let me know if it doesn't; it's a pretty simple spreadsheet made on Google Docs:
It's designed so that you just fill out a form after every class. (I know this works on an iPhone as well as a laptop, what about other phone types?) It updates the database itself and automatically appends new numbers into the graph. You can find that form here, feel free to try it out and then swap to the spreadsheet database and graph to see your responses tack on:
The form also carries out its own analytics, separate to any graphs you create from the data. You can find that in the menu under Tools>Form>Show Summary of Responses. In here it also compares attendance by student which might be useful if your aikido style grades by days at training.
(I'm pretty sure you can save it as a copy as it is with a Google Docs account. Let me know if not and I'll keep tweaking for a solution.)