If you incluse a text field identifying the trimester using a simple consistent code such as a four digit year plus a trimest indicator, e.g. 2012T1, you could the use only 12 calculation fields plus a compound key to keep track of every weekof every trimeseter in your database.
If the trimesters are equally spaced throughout the year, you could do a calcluation based on the date. But somehow I doubt the school system exactly breaks evenly spaced trimesters. I would probably create a separate table indicating the ending date of each trimester and have a relationship with the date that looks for the next trimester ending date and give the corresponding trimester field, which could be as DABrant says, something like "2012T1" or whatever works for you.
If you'll email me, I'll send you this Attendance.fmp12 file.
Thanks DABrant & Taylor.
Its a beautiful day here in COlorado. I had to get outside a bit.
I'll certainly need to study what you guys have suggested.
I forgot to mention that I have the 12 calc fields because i'm charting the total of each week.
Right now it resets at the beginning of each trimester.
But I'll study what you've suggested.
Let me get back to you.
Better yet, have a calculation that adds the week to Trimester and Week together so you can group them for your chart such as "2012T1.03" would be the First Trimester of 2012 and be week #3. Here is how it would work. The bottom part shows Attendance where you just put in the person's ID and the date, and on the far right, it puts the Trimester.Week calcluation. You can then chart the Trimester.Week easily.