Running Total

[mikedd]

Hello, I am a new user of OpenOffice.
I am trying to create a simple spreadsheet that will keep a running total of a given item.

For example:
In cell A1 through cell A2 are quantities of the item
In cell A3 amount of the item used (therefore subtracted)
In cell A4 amount of the item purchased (therefore added)
In cell A5 running total

My main problem is being able to enter the same number (as the existing number) in
cell A1-A2 or A3 and have the total update.
For example if there is a quantity of "1" in cell A1 and I enter the number "1" again the total does not update. It does not recognize the change.

Another problem is having cell A3 subtract from the total.
I know that I could enter a negative number but I would rather be able to enter a positive number and have that cell subtract from the total.

Any help is greatly appreciated.