quick overview :

Portable Type instruments are Electrodynamometer type instruments. They can be used in Single Phase, Three Phase Three wire and Three Phase Four wire systems, and are designed to be used in horizontal positions. Electrodynamometer Type Meters Rated Accuracy : ± 1.0% of full scale value as per ISS 1248/84 between 10% to 100% of the scale  for Single phase UPF Wattmeters : ± 1.5% of full scale value as per ISS 1248/84 for Three Phase Wattmeters : ± 1.5% of full scale value as per ISS 1248/84 for 0.2 P.F. (LPF) Single Phase     Wattmeter : ± 3° (Electrical) as per ISS 1248 for Power Factor Meters Note : All Wattmeters are calibrated at cos f = 1 and Varmeters at sin f = 1 : All Low Power Factor Watt meters are calibrated at cos f = 0.2 lag