A NMR experiment with cycling of a magnetic field is described. In this experiment alternate the standard cycles of field variation and cycles with preliminary inversion of the longitudinal magnetization by means of a 180 grade pulse. On the base of the Bloch equation solution it is shown that in this case the additive corrections to the measured value of magnetization conditioned by a finite time of field switching are mutually compensated. Application of the method developed permits to simplify the experimental data processing in the case when the spin-lattice relaxation time is comparable with the field switching time.