stock control

Hi all thanks for accepting me to this forum your help would be much appreciated

im currently trying to create a spreadsheet for fuel control stock for 3 different outlets on the same site using the meter readings collected each morning each outlet has its own workbook and a fourth workbook is an overview of the previous 3 for the accounts team showing year on year and graphs and data so far so good.
but i have been asked to produce a stock tab where it will automatically display the current dates stock is there a formula for this

kind Regards
Steddas