I don't think there is a way to use the Limit down at the Activity level in overage calculations.
If you want to have adjustable time periods, you can set up a new table called Date Selection, with a single record. Set up two fields for start and end dates. It will be the only record so Record ID =1.
link that in a relationship to all activities with a reference field which is a formula that calculates to 1.
That will allow you to create summary fields where the dates fall within the Date Selections.
I suggest that you show the overage report an a Report Link right on the Date Selector Record, so it's obvious what the selected dates are. Or else also link it to the Parent Company and/or Companies to b3 able to show the date range on the reports.
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Mark Shnier (YQC)
Quick Base Solution Provider
Your Quick Base Coach
http://QuickBaseCoach.commarkshnier2@gmail.com
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