Abstract: A method of mass spectrometry and a mass spectrometer for the analysis of a sample, the mass spectrometer comprising means for producing ions from the sample and a magnetic sector for analyzing the ions, wherein the magnetic field of the magnetic sector is generated by passage of a magnet current controlled by a digital control signal representative of a sequence of integers generated by a computer. According to the invention, means are provided for generating the magnet current in exponential relation to the sequence of integers. In contrast to prior spectrometers, the invention provides peak switching and mass selection across the mass range with a constant number of integer steps per mass peak, thereby facilitating the digital selection of any particular mass peak, particularly those at low mass.