Datums Required for Hole Position

[shaun8567]

I have what I hope is a pretty straight forward question. When placing a hole position tolerance, are 2 or 3 datum references required?

Take the drawing below:

If the hole is a through hole, does the call-out need to reference Datum A? A primary to B and a secondary to C leaves one DOF free for the hole to move (translation in and out of the screen).

 

[pmarc]

I am just curious whether OP got an answer clarifying his doubts...