Abstract: An automated cartridge library (30) has plural cartridge receiving units which are precisely locatable so that a transport device (300) can accurately move a cartridge (90) between at least two of the cartridge-receiving units. The cartridge-receiving units and/or calibration cartridges inserted therein have an indicia (190) which is of contrasting reflectivity, the indicia having at least two sides (191, 192) which meet at a vertex (193). An illumination source (340) on the cartridge transport device makes two sweeps (Y1, Y2) of an illuminating beam over the indicia. Illumination transitions as detected by a sensor (350) during the two sweeps are used to determine a location of the indicia vertex (193). In the case of a cartridge-receiving unit being a multi-celled cartridge magazine, a rear wall (220) of the magazine has an aperture (222) for each cell.