During a periodic calibration, there is a process where the reference strip is scanned and the measured output from {HEAD ~ the scan} is compared to {TAIL ~ a reference value} that represents the expected value corresponding to the reflectivity of the reference strip 
is compared to
During a periodic calibration , there is a process where the reference strip is scanned and the measured output from { HEAD ~ the scan } is compared to { TAIL ~ a reference value } that represents the expected value corresponding to the reflectivity of the reference strip
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH