A device that works by comparing the mass of an object to a known mass is called a balance.

There are different types of balances, including:

* Beam balance: This classic type uses a lever with a known mass on one side and the object being weighed on the other. The beam balances when the masses are equal.

* Spring balance: This type uses a spring that stretches or compresses in proportion to the weight of the object.

* Digital balance: These balances use electronic sensors to measure the force exerted by the object and display the mass digitally.

All of these balances rely on the principle of comparing the mass of an object to a known mass to determine its weight.