Jeff wrote on 8/3/2017 1:17 PM:

You don't understand the meaning of "phase". If you said the two
frequencies were never the same I would agree.

Phase is fundamentally linked to frequency.

The slave pendulum runs slower than the master with the intermittent
impulse to adjust the phase. The relative phase varies with time as a
sawtooth function and so at some point the phase *must* be aligned as the
slave passes from being ahead to being behind.

That is a ridiculous statement, if it were true you could say that any 2
random signals were 'in phase' just because at some point in time they both
had the same phase angle.

Not sure if you are referring to the Shortt clock or the PLL. But the
statement applies equally to both. There is no magical stability in the
PLL. It is a control loop and as such the thing being controlled will
*never* remain in phase or at the same frequency as the reference.

--

Rick C