52-week moving average without fixed entry count
I have all our sales data one line per line item (multiple lines per transactions). I'd like to create a moving weekly average (52 weeks) to give a better view of trends letting the moving average "correct" for seasonality. Because of the data structure I can't count entries (I don't know how many entries go into each week). Is there anyway to do this in Filemaker? I'd essentially need to have each graph entry be the average (or sum) of all sales that fall between two rolling dates. I'm not even sure how to create a new table with that type of information.
I know Filemaker isn't a statistics program, but having some more stats features would be nice :-)