Please let me know what factors should be measured to assertain the capacity of a AHU or a Packaged unit. What does it mean by on coil temperature and off coil temperature ?

Coil temp. should be 17 to 20 degs. Between supply air temp and return air, on a
r-22 system and 22 degs. On r-410 system if blower is set for right amount of air.. effec. Is tested at manufac. Can be found in a ari book.