simple sum in Excel but replacing one of the addends in its own cell

Question

Am an Excel novice and have looked in several MS office books I got from the library but none say how to do the following, and I've performed a couple of general internet searches to no avail as well as here. If this question has already been answered here, please forgive my inability to find it and post the link; I will be most grateful.

I have a sheet in which I have cell A1 and A2. Both contain positive integers. What I need the sheet to do is this: whenever a new number is entered in A1, this new number will add itself to A2 and then overwrite the figure in A2 with the sum.

All the directions I can find require that there be a third cell in which the answer will appear, but I can't revise this spreadsheet to accomodate that possibility. The sum must appear in A2. This is the way the boss wants the spreadsheet to look, and he won't agree to change it; it fits his needs as it is (obviously he doesn't have to enter the numbers!). So currently we are doing the addition manually and overwriting A2 (and other similar sets of cells in subsequent rows) by hand, but it would sure be nice to automate it.

Is there a way to do what I want, and also to retain the formula in cell A2 when coworkers who also enter data into the sheet accidentally do it the old way and enter a figure into A2 manually?

Answer 1

Is the value in A2 constant for each row? For example, if A2 is always 30 for particular row, you can just use =A1+30