add/subtract when typing into same cell

Is there a formula or something which will let a cell remember the value that was previously in that cell and then when you type a new value into the same cell will add or subtract what you typed in from what was originally in there?

I.E. Cell contains 10, and I type -5 into that cell and it automatically changes the value to 5.

seems like it would be easier than pulling out the calculator each time to update totals or to make another column just see what the new total is and then having to copy that back into the cell. Here's what I'm basically doing now:

Week 1 - 10 -5
Week 2 - 10 5
Week 3 - 15 20
Week 4 - -5 15

So you see, each week the left number is changing and the right now is a running total that either increases or decreases based on that left number.

Originally Posted by davesexcel

Here's a little vba code you could use

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right click on the sheet tab and select view codes
copy and paste this code there
when you change anything in range A2:A20 the next cell to the right will change accordingly

thats pretty nifty, how could i change it to target a certain cell instead of just the one to the right?

Just noticed that its changing the values for every other cell all the way across the worksheet. Is there some way to get it focus just on changing two cells the right of the one I'm typing the number into?

In the first column, I'm basically putting in a weekly dollar amount, and the second column that is being modified by the code is to show the dollar amount that needs to be recovered should that dollar amount in the first column be negative or lost revenue. So if that first column is a positive number then there is no money that needs to be made up so the recovery column needs to be zero because I don't want it to reflect that positive amount under recovery.