In the Microsoft Visual Studio series, you can set a checkbox to be greyed in its initial state, to indicate it hasn't been set. When clicked, it can only then be set to checked or unchecked. You'll have probably seen them around the windows control panels.
Obviously this can't return a "real" boolean value - it returns 0 for unchecked, 1 for checked, and 2 for greyed. However I find it quite useful.
You know what's coming next 🙂
Can it be done in Labview?
Cheers
Joolz