The models are selected for the unknown standards and performance data for {TAIL ~ each different calibration standard} of the set are measured by {HEAD ~ the test system} 
The models are selected for the unknown standards and performance data for { TAIL ~ each different calibration standard } of the set are measured by { HEAD ~ the test system }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD