Checkbox value in a custom ribbon

I have created a custom ribbon including a checkbox with a callback to
set its value in a public variable. The checkbox value is LATER used
as a parameter in other code. However I have found the scope of the
variable can be lost (e.g. if you change code in the VBE), whilst the
checkbox value remains. I therefore need a way of ascertaining the
value of the check box directly (no variables that can go out of
scope)

The GetPressedMso command seems promising but I have no idea how to
use..... any ideas greatfully received.

Thanks
John