How does 1PPS align with GPS time?

The receiver will continuously steer the phase of the clock to maintain 1PPS as close as it can to GPS time. The NovAtel 1PPS specification is less than 50ns to within GPS time, but typically it less than 20ns as long as the receiver clock status remains in FINESTEERING. It will not accumulate error unless the receiver has problems maintaining lock to GPS satellites. In this case the receiver's clock state will change to FREEWHEELING. There is no phase jitter in the 1PPS output. The 1PPS is steered through an analog circuit with 2-3 minute time constant and is in a bound of about 20ns (after the receiver is in FINESTEERING). The phase of all the clock terms are bounded by the clock steering bandwidth to within 50ns (95% of the time). The analogue 2nd order steering time constraint is in the order of a few minutes. The frequency of the on-board oscillator is adjusted very smoothly to maintain lock to GPS. We do not slip cycles to keep aligned. You can monitor the clock steering error feedback quantity through the last two parameters of the output message log CLOCKSTEERING. Look for the Range Bias and Range Bias Rate terms. These are our instantaneous measure of the clock offset and drift in units of meters/second. These should track to zero as the clock is steered to GPS. If the receiver is unable to control the frequency of its oscillator, these terms will ramp up and you can use them for your quality control. You can also extract the clock offset term from the TIME message. This is in units of seconds. The clock offset term is a heavily smoothed version of the instantaneous Range Bias terms.