Whitworth millionth measuring machine in a case for comparing components against standard inch bars; made in 1855.

Using this machine to compare standard inch bars, Whitworth claimed that he could detect the lengths of the bars to within a millionth of an inch. This claim seems exaggerated since even minor variations in room temperature would affect its performance, and the National Physical Laboratory has shown the claims to be untrue. An earlier machine of this type was displayed at the Great Exhibition of 1851.