A)Spring control method:
1) The spring control meters can be used in any position.
2) In some instruments springs can be used as current leads.
3) As springs are light in weight, practically there is no increase in weight of the moving system hence high torque to weight ratio.
4) Controlling torque can be adjusted easily.
5) Scale is uniform.
1) Temperature change affects spring length causing change in magnitude of controlling torque.
2) Accidental stress in the springs may damage them & spring get a permanent set if stressed beyond their elastic limit.
B)Gravity control method:
1) Simple and economical method.
2) Unaffected by temperature changes.
3) Not subjected to fatigue.
1) Instrument has to be kept in vertical position.
2) Scale is non-uniform.
3) Control weights add to the weight of instrument.