The Quantum Magnetometry Laboratory produces the processor Overhauser magnetometer POS-1 since 1998. The magnetometer is a precision instrument for measurements of the geomagnetic field modulus with sensitivity up to 0.01 nT at an operational cycle of s. Besides the field measurement the POS-1 has additional possibilities for continuous monitoring of the factors affecting its functioning. A statistical analysis of digitized periods of the nuclear precession signal in a single measurement gives with good accuracy the signal to noise ratio, the level and character of noise and the dynamics of period (frequency) changes. In particular, the knowledge of these parameters allows one to estimate the device sensitivity and the field behavior during a measurement, in fact to carry out the additional control for both the magnetometer and the ambient magnetic conditions.