Final answer:
A triple beam balance is used to measure mass by adjusting the sliding weights on the beams until the pointer is at zero.
Step-by-step explanation:
The instrument used to measure mass is called a triple beam balance. This type of balance consists of a lever system with three beams, each with a sliding weight. The object whose mass needs to be measured is placed on the pan, and the sliding weights on the beams are adjusted until the pointer is at zero. The sum of the weights on the beams then gives the mass of the object in grams.