Three stage checkbox?

[Sarah Reichelt]

Hi All,

I have a need for a three-stage checkbox, in my case signifying 
"Definite yes", "Definite no" and "Don't know yet". This needs to run 
on Macs only (OS 9 & X). I know that on Macs, you can have a checkbox 
that is either empty, ticked or has a line through it. If I could get 
those three options, I'd be fine but does anyone know how?

Failing this, I guess I'll have to use normal buttons and switch their 
icons instead, but a series of checkboxes is much easier to read & set.

TIA,
Sarah