The Eichstrich
All cold drinks in bars and restaurants are sold in glasses with a calibration mark (Eichstrich) that is frequently checked by the Eichamt (~ Bureau of Weights and Measures) to ensure the guest is getting as much as is offered in the menu. The Eichamt is a public authority controlling all measurements in sales, health care and so on, i.e., each scale in a German butcher shop or physician's office carries a stamp from the Eichamt, including a date of expiration, to show the weight is correct.
If the liquid of a served drink is below that line, the guest may refuse the drink or require a correctly filled one. A common rule for beer — with foam — is that the liquid-foam-line must not be more than one centimeter below the Eichstrich, otherwise a Munich resident could refuse the Maß at the Oktoberfest.
Read more about this topic: German Cuisine