A balance scale is the instrument used to compare the masses of two objects.

Here's how it works:

* Principle: A balance scale works on the principle of equilibrium. When the masses on both sides are equal, the scale will be balanced.

* Mechanism: It consists of a beam with a pivot point in the middle. Pans are suspended from each end of the beam.

* Comparison: You place one object on each pan. If the scale tips, the heavier object is on the side that goes down. If the scale remains balanced, the objects have equal masses.

There are different types of balance scales, including:

* Triple beam balance: Offers a higher level of precision.

* Electronic balance: Uses sensors and displays the mass digitally.

Let me know if you have more questions!