Observations on stability measurements of commercial atomic clocks

Besides the known effects of temperature and aging, abrupt changes in barometric pressure or in the Earth's three dimensional magnetic field, occuring typically every 100-800 hours and lasting for 20-200 hours. Cause unpredictable 10-100 ns cesium clock deviations in commercial equipment. An air pressure increase of 100 Pa is suspected to induce a 1.2 ns clock bias whereas observations indicate that a 50-200 nT H-field z-component of a magnetic burst initiates in an other design a positive or negative drift having an absolute value of the order of 0.3 ns/hour. Measuring techniques, based on various GPS Disciplined Oscillators, require the extension of similar recordings well over 1000 hours due to internal GPSDO anomalies which exceed 20 ns from the mean timing difference and may have a period of 500-700 hours.