Unique Calibration
The Emissions/CAFE/CO2 Compliance Department is responsible for assigning these calibration numbers. Unique calibration identifications are assigned to cover similar vehicles to differentiate tires, drive configurations, final drive ratios and other calibration-significant factors.
These two characters are chosen by the analyst to provide identifiable information unique to each calibration. For example, using the number 2 to denote a two-valve engine versus using the number 4 to denote a four-valve engine, offers an easily identifiable difference.