Abstract: A compact rotary instrument for accurately measuring small movements of a machine tool leadscrew, the instrument having one continuous decimally divided scale which indicates the measurement in either the metric or the inch system as selected by an operator. The instrument encloses a gear system which can be changed from a direct drive condition in which the rotary motion of the leadscrew drives an annular scale at a 1:1 ratio to an indirect drive condition in which the rotary motion of the leadscrew drives the scale through a gear train having two externally formed ring gears and two pinion gears carried on a stub shaft, at a 1.27:1 ratio. The selection is by means of an annular rotatable selector having two spaced marks formed thereon against which the scale can be read by an operator, the rotational positions of the selector and the spacing of the marks being such that when direct drive is selected only one mark is visible by an operator and when indirect drive is selected only the other mark is visible.