The process by which one determines a woman's bust strictly by appearance from a distance. This method is also name as BET for short.
The method may involve how much the breast protrudes from the clothing that is worn on the individual. This gives the observer an indication of the volume of the boob.
Further factors may include the height or weight of the person.
Dude 2: I dunno man, but let's use the Boob Estimation Technique!
Dude 1: BET? You're on!