Phasemeter output waveform resolution

Phasemeter output appears to have phase drift

The Moku:Lab Phasemeter instrument can generate an output waveform.  This waveform is generated by a NCO ('numerically controlled oscillator') with an internal Moku:Lab reference of 10 MHz. Over a long period, it is possible to observe a steady slow phase drift when comparing this output waveform with another signal.  

The precision of this output waveform is defined by the resolution of the NCO thus :

phasemeter resolution output formula

Any mismatch in the signals frequency leads to an observable but slow drift of phase.