The pendulum gun was introduced in answer to the problem of tracing the co-relation of pressure, velocity and recoil when testing cartridges. In considering this problem, the designers had to find a way of translating recoil into an absolute measure, or in other words, to express recoil in units which were equally applicable, whatever the weight of the gun. The method of suspending a gun by four stranded steel wires almost entirely eliminated friction and ensured that each successive swing of the gun on firing was less that the previous one by a very small fraction, thereby ensuring a greater accuracy in the calculations necessary for measuring the momentum on firing