A conversion unit for attachment to a machine tool constructed to operate normally in English units of measurement so that the machine tool may be used directly in metric units, or vice versa. The unit comprises an externally toothed gear wheel which may be fitted to a screw of the machine tool to turn with it, and an internally annular gear eccentrically mounted to mesh with the other gear, the number of teeth on the gears being chosen so that the correct conversion ratio is produced, the measurements being readable from graduated scales. BACKGROUND OF THE INVENTION.
A conversion mechanism is attached to a speedometer in such a way that the input into the speedometer can be mechanically altered to establish a conversion ratio between a first system of units and a second system of units and the speedometer is indexed to display the speed measured in either system of units. The conversion apparatus is switchable between two modes to cause the speedometer to register selectively either of the two systems of units, and the apparatus is designed to be interposed at any point along the mechanical drive or input for the speedometer.
