Subtracting from Different Dates
 

I have a spreadsheet that I use for inventory. I add a column and print
every week using a simple macro. I have different years' inventories on
different worksheets. I would like to create a chart by product that shows
how much of each product was used by month so that I can compare monthly
usage between different years.. The inventories are done weekly (usually,
but not always on tuesdays).

TIA