— The issues of determining the momentum of charged particles at the focusing double-arm spectrometer (FODS) are discussed. The coordinate detectors are located at the exit from the analyzing magnet, while a profilometer of the center of gravity of the beam at the target during an accelerator cycle is at its entrance. ANSIS finite-element analysis software is used to obtain a regular grid of magnetic field vector values measured by the Hall sensor in a part of the magnet. The charged-particle momentum is determined based on the algorithm of decision tables with a polynomial approximation. Tables are produced by the Monte Carlo method by reconstructing the motion of a particle with a prescribed momentum in the magnetic field. The accuracies in determining the particle momentum and the particle production angles while accounting for the contributions from multiple scattering, measurement errors, and approximation uncertainties are presented. The distribution of the reconstructed trajectories in the target and the momentum spectrum of particles are shown.