The closest I can come to your solution is this:
Dim x As Integer
Private Sub Worksheet_Activate()
x = Range("A2").Value
Private Sub Worksheet_Change(ByVal Target As Range)
If Intersect(Target, Range("A2")) Is Nothing Then Exit Sub
Dim y As Integer
y = Range("A2").Value - x
Range("B3").Value = Range("B3").Value + y
Paste the code under the sheet it is for. This is the way it works:
Make sure you have at least 2 sheets.
Go to sheet 1 and enter 50 in A2 and 100 in B3.
Now go to sheet 2 and then back to sheet 1. Excel now has the value 50 in it's memory.
Now change 50 into 70 in A2 and Excel will subtract the value in it's memory (50) from the new value and add the difference to B3.
To change Excels memory from 50 to 70, you will need to go to sheet 2 and then back to sheet 1.
Otherwise you will have to think of another way of doing this, like using another cell for the increment and then add that cell to both A2 and B3.
Monday, Tuesday and Thursday are usually the days I'll respond. Bear this in mind when awaiting a reply.