Multiply cells then perform IF else

Hi all,

Struggling with working this one out, I managed to get the code working with one sub calculating the cell multiply on a loop and then another sub performing the IF but because excel won't recognise VBA cell changes it wasn't triggering the second piece of code so now I'm trying to combine the two.

This is what I currently have:

Object:

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Module:

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Whats the best way to combine these so it loops the multiplication and then performs the IF statement on Cells(i,23) every time the user updates?

Many thanks in advance

Matt