The load gauge is an accessory or optional item on all aircraft jacks. It is not recommended for axle jack applications where the jack is subject to frequent high speed towing or other conditions that would induce excessive shock or vibration. Load Gauges are usually specified on tripod jacks that are moved infrequently, towed at slow speeds (less than 5 mph) and rough or uneven surfaces are avoided. A load gauge does not accurately measure load. It’s only purpose is to provide an approximate indication of load. (Most aircraft jack load gauges are hydraulic pressure gauges that measure the internal fluid pressure of the jack. Jack plunger(s) seal friction, mechanical side load on the jack plunger(s), weight of plunger(s) and the accuracy of the gauge itself all contribute to reduced accuracy.
For additional information see Load Gauge Technical Paper (PDF)