Detecting Column selected from cell or range of cells

I am trying to set up a macro to ensure only a cell or cells in Column C are selected by the user (Mouse).
The problem I am stumbling on is extracting the Column letter ("C") from "myRng".

I seem to be reading the cell contents rather than the cell or cells range.
Example cell contents:

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Any help is appreciated.

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(Acknowledgement: Most of the Macro is from a forum member whom helped me out)

Some examples of getting column info from a given range:

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Thank you for clarifying what I was doing wrong.
With the qualifier, I am still not capturing the Column Letter.
Which is where I am stuck.

Attached is a sample excel XLSM file.

That will be because 'Left(myRng.Address, 1)' = $

Try:

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End column would be:

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If you wanted to use the other method then you would need to turn off the absolute part of the range.address:

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I would not recomend this as what if the column in question was AA? The second A would be lost.