A positioning goniometer or goniometric stage is a device used to rotate an object precisely (within a small angular range) about a fixed axis in space. Its appearance is similar to that of a linear stage

Linear stage

A linear stage or translation stage is a component of a motion system used to restrict an object to a single axis of motion. The term linear slide is often used interchangeably with "linear stage", though technically "linear slide" refers to a linear motion bearing, which is only a component of a...

. However, rather than moving linearly with respect to its base, the stage platform rotates partially about a fixed axis above the mounting surface of the platform. The distance of the center of rotation from the platform mounting surface is often chosen so that two different goniometer models may be stacked in an X-Y configuration and both stages will rotate about the same point. Positioning goniometers typically use a worm drive

Worm drive

A worm drive is a gear arrangement in which a worm meshes with a worm gear...

with a partial worm wheel fixed to the underside of the stage platform meshing with a worm in the base. The worm may be rotated manually or by a motor as in automated positioning systems.