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

Here are some common types of balances:

* Beam balance: This classic balance uses a beam with a pivot point and two pans. The object being weighed is placed on one pan, and known weights are added to the other pan until the beam is balanced.

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

* Electronic balance: This type of balance uses sensors to measure the force of gravity on the object, and then calculates its mass.

Let me know if you'd like to know more about any of these types!