The holder with the integrated glass standard is
used for calibration. Always keep the measurement
unit in the holder. This protects the measurement
optics and ensures that the standard is always at
hand.
If you have several devices of this type, you must
put the unit in the holder which belongs to the unit
(see the serial number).
Make certain that the standard is clean and
there are no cracks on it.
When you place the device in the holder, make
certain that it ships firmly into place.