|Do the numbers change more than once a day? If so, should each change be counted?|
Are you looking to check the numbers in a specific column or in multiple columns? (Details would help.)
Will the spreadsheet be opened every day in order to take the count or might it be closed for e.g. 3 days, with those 3 days being assumed to remain either positive or negative, and therefore be counted as 3 days at one or the other.
My assumption is that this is going to need a VBA solution and that the date calculations will need to be done based on when the sheet is opened/updated.
The more details you can provide about what you are trying to do would help us design a solution.