Stackable rotary devices form a multi-position mechanical indicator for a portable data storage cartridge. Each rotary device is a right cylindrical section, and is separately rotatable in a chamber of the cartridge. A peripheral surface of the rotary device has an encoded pattern of 1) at least one cylindrical surface and at least one facet interrupting the cylindrical surface, or of 2) readable indicia, located at various angularly spaced rotational positions. At differing rotational positions of the rotary devices, at least one or none of the facets or readable indicia are positioned at an exterior wall opening of the cartridge chamber.