Add 1 to target on double click, add 0.5 on shift + double click

Hopefully the title is relatively descriptive.
I currently have a relatively tedious task which involves slowly counting things. To make the process quicker I've used the following code:

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This works great (I imagine the nested ifs could probably be made more concise but I'm not too fussed about that)
Anyways, this may (is likely?) outside the scope of what VBA can do (or at least what I can do with VBA), but is there any way to add 0.5 instead of 1 if I've got shift (or any other specified key) held down?
Your help is much appreciated.
Lady Marmalade

Originally Posted by sweep

Hello,

Chip Pearson has an article on his website about testing key states;

http://www.cpearson.com/excel/KeyTest.aspx

It worked perfectly! Thank you so much; I had to disable the Alt + Click function of excel which automatically opens the research pane, but it's brilliant.
Quick unrelated question - your signature says to never merge cells. Care to explain why? Just for my general knowledge
Thanks