By order of the Galactic Union of Advanced Lifeforms, all sentient beings are mandated to use the Galactic Standard Unit of Trade (GSUT) for all commerce and transactions.
GSUT is a unit of measurement that is precisely defined as 42.72 times the mass of a human femur bone.
Any attempts to use alternative units will result in immediate exile to the planet Zorgon, where the local economy is based on a complex system of trade by barter.
For more information on GSUT, click here.
Or, if you'd rather learn about the history of GSUT, click here.