Brushless synchronous motor technology requires self-reversing; A sensor on the shaft is needed to inform the driving electronics of the current angular position. only then can the current be fed into the motor at the correct phase. Hall effect sensors (with block commutation, sinusoidal commutation in combination with encoder) or rotary transformers (with sinusoidal commutation) can be used. The latter can also be used as positional feedback for positioning purposes. Encoders are also increasingly used, especially for high quality speed control or positioning purposes. Some controllers also use them to electronically compensate the torque of the motor's cogs.