PERMANENT magnet instruments or PMMC are suitable for only DC measurements.In PMMC type instruments, defection is directly proportional to the current (θ ∝ I) HENCE these instruments have uniformly DIVIDED scales.The error due to the external magnetic field is called a stray magnetic field error. It is LESS in PMMC since a strong magnetic field is present inside.The cost of PMMC instruments is very high.Moving Iron (MI) type instruments can be used for both AC & DC measurements.Rectifier type instruments are used for both AC & DC measurements.Induction type instruments are only used for AC measurements.Thermocouple meters can be used for both DC as well as AC quantities.Note: In terms of accuracy PMMC meter has the highest accuracy. The order of accuracy is given below.Induction < Moving iron < PMMC instruments