GZG figs / mm scale

A quick question of scale --

When GZG figure scales are quoted in millimeters, is that the foot to 
eye distance or foot to top of head distance?  From what I gather, it's 
more common for the mm scale to refer to the foot to eye distance for an

average man, than for the foot to top of head distance, but that this 
does depend on the manufacturer.

Cheers,
--Jerry Acord
acord@imagiware.com