Abstract: An air-core gauge comprising two coils in quadrature has a driving system with switches on a junction terminal and end terminals of the two coils, and a drive circuit controlling the switches so that each terminal is selectively at either of two signal levels, with one terminal being connected alternately to the two signal levels with variable duty cycle depending upon the angle through which the pointer of the gauge is to be turned. For any given angle, one terminal is held at one level, another at the other level and the third is alternated between the two levels with appropriate duty cycle. Any angle of pointer deflection from 0.degree.-360.degree. can be achieved with just the two voltage levels and calculating the duty cycle from an appropriate function of tangent values of angles in the range 0.degree. to 45.degree..