I am trying to create a report that captures the value of our total open opportunities on a daily basis to report as a line graph. Weekly would be fine too. Any thoughts?
What you're looking for is an analysis of historical data, which can't be easily captured in a live-data system without causing significant stress on your database and performance. For use cases like these, I'd recommend a third-party Business Intelligence connector or working with a Sugar partner who can extract the relevant data at pre-defined intervals and design a custom report to your specifications.
As a manual solution, in the past, I've successfully created a graph like this using a spreadsheet. For smaller datasets, you can just have a scheduled report come to your inbox and manually copy the "snapshotted" data into your external report. For larger datasets, you could grab monthly or weekly backups of your database, extract the data you need, and then re-compile the external report as needed.
Another thing that may interest you (though not solve your original request) is the relatively-new ability to report on record change logs using Advanced Reports. I haven't played around with it much, but here is an intro to that capability: Reporting on Record Change Logs via Advanced Reports
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