Its called: Hi-profit-pour. from http://www.drinker.com

Hi-Profit-Pour™ measured pourers reduce liquor shrinkage substantially increasing your profits the day you put them on all your bottles. And they keep on delivering those profits, day in and day out.
According to Bevinco, an independent beverage inventory control service, liquor shrinkage losses averages 23% on liquor and can run over 50% in some bars.

Here’s how much over-pouring really costs you…
If your bar pours a 1 ½ ounce shot, you will get 22 drinks out of a
one liter bottle. If your staff over pours by one ½ ounce
on average, you’re losing 6 drinks per 1 liter bottle. Based on an
average cost per drink of $4 you’re losing $24 per bottle. That
translates into $288 per a 12 bottle case. and that allot of money especially if you think yearly.

Cheers!