What is free lift in pilot balloon?

The free lift of the Pilot Balloon is defined as the difference between the total lift and the weight of the balloon and its load. The free lift is really the net buoyancy of the balloon. Thus free lift is the force tending to drive the balloon (Hydrogen filled) upward, which depends upon the amount of hydrogen gas filled in it. If a hydrogen balloon is inflated until it floats with certain weight attached to it, than it indicates that the attached weight balances the upward force acting on it. This weight is called free lift of the balloon and if weight is removed, the balloon rises up (with fixed rate of ascent corresponding to weight attached while inflating).