When a materials testing machine is used dynamically, the force recorded by the load cell may differ from that experienced by the specimen. This error is caused by the mass of the load string, usually the grip, between the specimen and the load cell.

The equations of motion for a testing machine are developed and the parameters affecting the error are identified A system is described which removes the inertia error from the load-celt output by measurement of the acceleration of the mass. The effectiveness of the technique is assessed by the use of strain-gaged reference specimens, of different stiff- nesses, for comparison with the load-cell output. Two methods for calibrating the system are used and their merits assessed.