"Cal Error 4## Cell Change" — Check Aperture Setting. If set correctly, it may require service, possibly a cell problem. This error message (## may be any number between 01 and 16) in most cases requires that the instrument come in for service. It means, that the instrument is seeing less reflection on the white calibration standard than it originally saw (when configured at the factory).
Be advised however that there are several conditions that may produce these error messages. Before returning your instrument for repair please check all of the following:
The correct white calibration standard must be used.
Specifically, each instrument is "married" to a particular calibration plaque at the X-Rite factory. The absolute reflectance values of this plaque are programmed into the instrument's RAM memory as it undergoes final testing. Each plaque is serialized and the serial number of its matching instrument is hand-written on the protective envelope. The use of an alternative plaque may well fool the instrument into thinking that the ceramic surface has changed.
The calibration standard and instrument optics have to be meticulously clean and dry.
Blow out the optics with low-pressure, dry air and wipe calibration plaque with a soft, clean, lint-free cloth. Fingerprints, if present, may be removed with clean water or isopropyl alcohol. The surface of the plaque must be completely dry before measurements are taken.
Check the aperture setting in calibration, and make sure it is set to the size currently installed in the instrument.
In brief, most 900 series instruments have field interchangable apertures. A change of components must be matched with a change in instrument configuration (RAM settings). If none of this helps, the instrument must be sent in for service.