For the case of under water weighing, the buoyant force plus the force provided by the scale (apparent weight) must perfectly balance the weight of the object, as long as the person is holding still. ...For the case of under water weighing, the buoyant force plus the force provided by the scale (apparent weight) must perfectly balance the weight of the object, as long as the person is holding still. Measuring the weight and apparent weight of a body allows us to calculate its density because the buoyant force that causes the reduction in apparent weight has a special relation to the amount of water being displaced by the body.
