Understanding the functional behavior of precision engineering workers was the aim of studying the ultradian rhythms of HRV indicators to prevent man-made disasters. It was revealed that the higher the voltage of the functional state, the lower the heart rate indicators. The results established specify activation of the vagus associated with cognitive activity. Precision engineers used ultradian rhythms of HRV indicators and the Pareto law to assess the functional behavior of men. The results revealed that work activity negatively impacts the functional behavior and health of 58% of men, placing them in a group associated with human factors and man-made disasters.