As I recall, the Nav sends the value plus the units to the CheckControl display.

The units are in the navboot file eg:

001/0359 "km"
001/0360 "mls"
001/0361 "Consump."
001/0362 "l/100km"
001/0363 "mpg"
001/0364 "km/l"
001/0365 "Temperature"
001/0366 "°C"
001/0367 "°F"

The units are the same text that appears in the Computer display on the nav