Abstract: A portable metrological instrument for measuring surface finish parameters has a main housing which sits on a workbench. A slidable arm can be extended or retracted over the bench so as to move a stylus over a workpiece. The stylus is fitted to a gauge mounted to the end of the arm. The mounting includes a vertically movable slider which incorporates a mechanism for lifting the stylus away from the workpiece and lowering it back. The operation of the instrument is controlled by modular software which can be reprogrammed using an external device, and the machine is operated by a control panel on the housing or by an identical control panel on a remote controller. The gauge includes an inductive sensor, and the associated circuit includes automatically adjustable error canceling devices. The control system uses the sensed position of the arm to estimate the speed of the motor which drives the arm, avoiding the need for a shaft encoder on the motor.