subtracting total

I have a spread sheet that keeps track of indirect items. I have an On-Hand qty column and would like to know a formula that will allow me to add a column before the On-Hand that when a number is put in the new column, it will subtract from the On-Hand qty Column. It also has to remain the new number when the column is cleared.

Ex.
Initial) run Qty On-Hand
10

After run) Run Qty On-Hand
3 7

Next Day) Run Qty On-Hand
7