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