|First, a posting tip:|
To use the pre tags to align text in this forum, you have to use a "less than" sign before pre and a "greater than" sign after pre. The same is true for /pre.
It should look like this, but without the asterisks:
<*pre*> Your Text <*/pre*>
Second, I mentioned this in my last response, but you did not comment, so I will mention it again:
I see no reason to set the Target as A1 and then check to see if the Target cell Intersects with A1. Of course it does, because you set the Target as A1. To me, that appears to be a total waste of resources.
Please explain your reason for doing that. I'm willing to learn.
Finally, the reason your code freezes your system with =SUM(A2,A3) in C4 is because each time it places values in A2 and A3 the sheet recalculates, triggering the code to run again, which places values in A2 and A3, causing the sheet to recalculate, triggering the code to run again, and so on forever.
The way to prevent Event triggered code from continuously being triggered is to disable events while the code is running and then enable them again when it is done.
This code should work for you. You'll notice that I eliminated any use of Target because I do not believe that it is needed.
Private Sub Worksheet_Calculate()
Application.EnableEvents = False
Range("A2") = Range("A1") + Range("B1")
Range("A3") = Range("A1") - Range("B1")
Application.EnableEvents = True
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