How full is your glass?

Is your pint glass half full or half empty?
I've never worked out why we're so precious of some of our old imperial measurements. Especially when no one is quite sure how much a pint should actually be. Wikipedia has at least 7 different definitions of it.
So when I ask whether your pint glass is half full, is it 284ml, 280ml, 285ml, 213ml (S Aus.) or 225ml (US dry).
Now the one thing you can't argue about with metric measurements is that half of a 1/2l glass is always 250ml.