Excel help, constant running total

I need help with an inventory workbook our company has. We need it to have a running total of parts instock, and as we use the worksheet to input data, the inventory will change and then we have another sheet for output data that will tell us what parts we need or are short. The problem is we need to be able to do this process, clear the old entries, then start another job, but have the inventory counts to stay constant as they were changed from the last set of entries. Any thoughts.

Thanks,
Jim