Unable to fire Private Sub Worksheet_SelectionChange on user Input

Good Day All (Please see Most recent post below)

VBA Skill: Pretty Basic
Excel type: Excel 2010

Problem:
Range("A1:A10") is where my users will enter a text structure; 1.0, 1.1, 1.2, 2.0, 2.1 etc. If the user enters a text string that includes "0" then we would like the code to activate and place a formula Offset(0, 4) from the ActiveCell, the following code is cobbled together from various posts and works to some extent:

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This code activates if we have entered 1.0, 2.0, 3.0 etc however it only works after we return to the Cell (with Keyboard Navigation Keys), what do we need to do to make the code activate on "Enter" or when we leave the ActiveCell; i.e. User inputs 1.0 hits Enter, Tabs or Navigates using the arrow Keys Then Code Activates.

I wondered if the following would be more effcient than ActiveCell but i can't get it to work with the above code

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Any help will be gratefully received

As advised below; Apologies for delay, my work Internet is rubbish!
Test Macro Entry via VBA.xlsm

Change SelectionChange to Change.

I went back to the drawing board and support.microsoft.com and have come up with the following:

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Am currently trying to change the line

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to

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this is how i would expect it to look as a function =IF(RIGHT(A1,LEN(A1)-FIND(".",A1,1))="0","Do Nothing", "Add Formula as per ActiveCell.Offset")

Any help as always gratefully received

Got it

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should actually read

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less the: " "

Working Code So Far:

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You can replace Range(Target.Address) with Target.

not Range(Target) - just Target