The density or weight of a given volume of liquid is determined by using a mud balance.
The arm is graduated Specific Gravity and permits accurate measurements to within ±0.01 specific gravity.
The balance is constructed so that the fixed volume cup at one end of the beam is balanced by a fixed counterweight at the opposite end, with a sliding weight rider free to move along the graduated scale.
A level bubble mounted on the beam indicates when the system is in balance.