Something I've been doing more than once is to create a help table with dates running from 1.1.201X to 31.12.20YY.
It's a table having a date field for every record and a record for every day, encompassing 20 - 30 years from "now".
Once you have a structure like this you can define other fields and relationships to your existing data which will help you to evaluate all kinds of things. Graphs included.
Thanks for the help, siplus. That is what I ended up doing to achieve the chart portion, anyway. The beauty and pain of FileMaker is that there is almost always more than one way to accomplish something.
To paraphrase from a text book on managing projects that I had back in my college days:
Doubling the number of people does not cut the time to completion in half. There's some diminishing returns involved due to the fact that the more people you add to the team, the less productive they become as individuals due to the need for time spent in communication and coordinating between team members.
You probably knew that already, but just in case...