Canonically, onlookers will shout out the number of seconds the drinking participant drinks for before having to stop. If in a competitive setting, an agreement is commonly made beforehand about the pressure of beer coming out. The general pressure setting is for a high-pressure stream, as low pressure pours from the keg may lead to more of a variance in the amount of beer consumed in a given count.
Other forms of keg stands may be done, such as holding onto an object rather than being held aloft by people.