The tile with the label is the Instrument Standard and is used to standardize the instrument. This tile is provided with a Certificate of Traceability and has calibrated values assigned to it.
The tile with no label is the backing tile, that can used to keep dust or debris out of the view port when the sensor is not in use, or can be used as an opaque backing for translucent samples.
HunterLab recommends that you only use the Instrument Standard white tile for standardizing the instrument then return it to the calibration accessories box. We recommend that you then use the backing white tile for all other purposes associated with your products measurements.