Account for head, and spillage 'twixt bar and table, and it soon becomes clear that you don't have the full pint you paid for.

Banks's brewery embarked on a marketing campaign, based around the fact that their glasses are oversized, with a pint mark about 1cm from the rim. The slogan is "full pint guaranteed" (catchy, eh?) -- depending on what you're drinking, sometimes the pump even measures out an exact pint.