A balance measures the weight of an object or compares the difference of weight between two separate bodies. This measurement of weight can then be converted into mass, hence it is also possible to measure the mass of objects using a balance.
The weight of an object is different than its mass. Weight of an object is equal to the mass of the object times the gravitational pull of the earth. By measuring the weight of an object, its mass is easily calculated. Since the gravitational pull of the earth is always present, it is a convenient practice to measure the weight of any object and then, if necessary, calculate its mass.