Excel sum function

[sqrlb8]

I am having a hard time figuring out a formula. Here is what I need to do.
There are 2 sheets in my workbook.
Sheet 1 Cell A1. A value is inputed to this cell. Once it is added it is sent to sheet 2 cell A1.
Now what I need to.... I need to take out the value of Sheet 1 Cell A1 and input another value, BUT. The value in sheet 2 Cell A1 must keep its value and add the new value of sheet 1 cell a1.

Clarify here.
Sheet 1 Cell A1 = 20
Sheet 2 cell A1 would then = 20

Now reenter value for Sheet 1 Cell A1 = 30
Sheet 2 Cell A1 should then keep the value 20 but then add new value of 30.

How do I do this?

[Tom Schreiner]

Hi
I do not think this is possible with a function or formula...
This, however, will work for you...

Right-Click on your sheet1 tab,
Choose 'View Code'

Paste the following, as is, into the code window...

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Row = 1 And Target.Column = 1 Then _
Sheet2.Range("A1").Value = _
Sheet2.Range("A1").Value + Target.Value
End Sub

Tom