Scalar control of an AC electrical motor is a way to achieve the variable speed operation by manipulating the supply voltage or current ("magnitude") and the supply frequency while ignoring the magnetic field orientation inside the motor.[1] Scalar control is based on equations valid for a steady-state operation[2] and is frequently open-loop (no sensing except for the current limiter). The scalar control has been to a large degree replaced in high-performance motors by vector control that enables better handling of the transient processes.[1] Low cost and simplicity keeps the scalar control in the majority of low-performance motors, despite inferiority of its dynamic performance;[3] vector control is expected to become universal in the future.[4]