Most ISOCAM data products report wheel positions by their angular displacement with respect to some fixed and arbitrary zero position; the angular displacement is measured in step numbers 2.1. The calibration file CWHEELS gives the more descriptive names used among observers for the optical element in the path (such as `Hole', `LW10', etc) for each wheel position (Section 6.1.14). The correspondance between wheel step numbers and optical components is shown in Figure 2.5.