I have possibly screwed up in a big way.

In my spreadsheet I have assumed that records would be added chronologically
(as they should), and did not allow for the fact that people don't always do
as they should.

Which means, my little calculation in Cell C615 ( =D615-D614) could actually
return a negative number if the items were not data entered in Chronological
order.

I'm not sure whether the formula in Cell C615 should be altered to say- look
at the date in Cells D002:D2500 and find the one with a date nearest, but
less than cell D615- and subtract that date from cell D615 and return the
value to Cell C615--- or if I should somehow prevent records from being
entered out of order.

Any ideas or help would be very greatly appreciated.

Gina