i. Hysteresis: Hysteresis is due to magnetic effects of the metals. It gives the relation between field current and the output voltage. The magnetization of ferromagnetic substances due to a varying magnetic field lags behind the field. This effect is called hysteresis, and the term is used to describe any system in whose response depends not only on its current state, but also upon its past history.
ii. Drift:The gradual shift in the indication or record of the instrument over an extended period of time, during which the true value of the variable does not change is referred to as drift.