  We propose a new method for absolute momentum calibration of magnetic
spectrometers used in nuclear physics, using the time-of-flight (TOF),
differences of pairs of particles with different masses. In cases where the
flight path is not known, a calibration can be determined by using the TOF
differences of two pair combinations of three particles. A Cherenkov detector,
read out by a radio frequency photomultiplier tube, is considered as the
high-resolution and highly stable TOF detector. By means of Monte Carlo
simulations it is demonstrated that the magnetic spectrometers at the MAMI
electron-scattering facility can be calibrated absolutely with an accuracy
$\delta p/p\leq 10^{-4}$, which will be crucial for high precision
determination of hypernuclear masses.
