This is pretty cool, what you have going on with the X toggle.

Have you already deciphered how it works (and why the Instr function test
works) or was your statement a request for an explanation?

Just curious why not use Target instead of ActiveCell, and why
not fully qualify Range("A1:A10")?

Yes, I should have used Target instead of ActiveCell. When I first developed
the code, I simply used a Sub Test() procedure to do it, hence the use of
ActiveCell. When I saw that you had used the DoubleClick event, I then
changed to that header also, copied my working code into it and forgot all
about changing ActiveCell to Target.

I'm not exactly sure what you mean by "fully qualified"; could you please
explain. Just so you know, the reason I am unsure of what you mean is that,
as you might be able to tell from my sign-on name, I come from (well,
actually, still actively participate in) the compiled VB world and, while
I've been attempting to help out here in the Excel world for a number of
months now, some terms and reference are still unclear to me. I am
attempting to learn them as I come across them, but I am not sure I have
seen the term "fully qualified" with reference to a Range yet.

Rick