Abstract: A digital instrument produces a continuous digital readout representative of the linear movement of a member positioned by a rotatable shaft. The instrument comprises equally spaced markings formed on an element carried by a bushing intended to be secured to the shaft. Sensing means cooperate with the markings and produce an output pulse in response to the passage of a marking past the sensing means. The output pulses are counted by a reversible digital counter the count of the counter being displayed by digital display means. The electronic circuitry is carried by two printed circuit boards each of which supports a bearing for the bushing. A fixed casing fixedly supports the sensing means, the counter, the display means and the printed circuit boards.