Stephen POWELL wrote...
....
Since Monday I have been struggling with a workbook that seems
self-corrupting.
My workbook has about 100 worksheets; each worksheet contains an
amortization schedule for the debt on a vehicle.
All amortization schedules have an identical structure.
Size of workbook is just under 30MB.

Amortization tables are generally pretty simple, and a single one
shouldn't take up 300KB (30MB / 100). What's in these worksheets? How
heavily formatted are they? My point in asking is that no matter how
much RAM you have, Excel works poorly with workbooks larger than 16MB.

That said, if you need access to all amortization table values at each
payment for each vehicle, you should be using a proper database rather
than Excel. You may want to use Excel to create the amortization table
values for each vehicle, and merge them into a common database table.
As long as vehicle ID and payment dates are fields along with principal
and interest payment amounts (total payment amount is unnecessary as
it's just the sum of principal and interest payment amounts), you can
generate entire amortization tables for each vehicle as well as
calculate principal, interest and total payments for all vehicles in
any given period.