Magnetic petrol gauge with cork float and dial indicator, for motor cars, made by Simms Motor Units (1920) Ltd., c. 1926

A gauge with cork float and dial indicator, for measuring the level of petrol in a motor car petrol tank. This type of instrument was invented by T. Martin in about 1912 and this example was made by Simms Motor Units Ltd., London, c. 1926. The dial contains a pivoted magnetic needle which acts as a pointer. As the level of petrol in the tank falls, and the float with it, the motion of the float arm rotates the magnet and with it the pointer.