When the instrument is first turned on it must be nulled (zeroed) before taking measurements. To perform this task proceed as follows:
Nulling the instrument
*Once the unit is reading 0.00 without any film the "NULL" button should NOT be used again until the unit is turned off.
Calibrating / Setting the instrument's slope
5. Once the Cal step is in agreement read the additional steps to see if you have a Linear unit. They should now hold the +/-0.02 tolerance to the strip.
NOTE: When measuring density values above 2.50D, care should be taken that the reading head light seal is completely on the surface of the film being measured. Always measure density with the film emulsion side up.
If the unit does not read zero after several attempts at nulling, and the light source and power supply have been verified; there is an internal failure and the unit must be returned for repair. It is recommended that the calibration / verification be performed once a week. More frequent verification can be performed if required by local regulations.