A new model of a quantum magnetometer based on the principle of Cs-K tandem was developed and experimentally tested. The specific features of the magnetometer are a single absorption cell containing Cs and K vapors, digital synthesis of the potassium resonance frequency by multiplying the cesium resonance frequency by a conversion factor (the ratio of the atomic constants), and the use of four-quantum resonance in potassium atoms. Device readings were found to be insensitive (within 10 pT) to variations of the main operating parameters even if the variations go far beyond the normal service variability.