Poole's Auxiliary Compensation.This is the first form of auxiliary compensation known to have been applied to a compensation balance.In its simplest form, which has been used in a large number of chronometers, it consists simply of two small screws carried upon rigid arms united to the cross-bar of the balance, and so adjusted as to meet the rims, near their roots, as they move outwards in low temperatures. The effective lengths of the latter (and accordingly, the motion of the weights which they carry) is thus reduced slightly below its normal amount. This action is made use of by adjusting the chronometer fitted with such abalance to keep correct time, say at 90° and 60°, which would normally cause it to have a considerably increased error at 30°. The action of the check screw, however, counteracts this.The practical effect of the device is then, to halve the middle temperature error between the two standard temperatures, and greatly to reduce the error which would normally be produced in low temperature by this adjustment. Balances of this pattern are simple to make, and their popularity may be ascribed to this reason.