A working standard, usually a white ceramic plaque plus a black trap and sometimes a green or gray tile, kept beside the instrument for routine checks. Testers read it at shift start and compare it with its logged value; drift beyond the lab's limit triggers a full restandardization against certified standards. Fingerprints, chips and dust on the tile cause more false alarms than the instrument does.
Cal tile is reading three tenths low on brightness, wipe it down before you call the instrument guy.
Hold the tile by its edges and store it face down in its case; one greasy thumbprint can move the brightness reading.
Also heard as
- the tile
- working standard
- white tile
Related terms
Reference standard
Certified material with assigned reflectance values that transfers a measurement scale to a working instrument.
Spectrophotometer
Instrument that measures reflectance across the visible spectrum and computes brightness, whiteness, opacity and color.
UV calibration
Setting an instrument's ultraviolet content so fluorescent samples read as they would under the specified illuminant.