On Sun, 8 Nov 1998, Reginald Neale wrote:

> I've just been re-reading a twenty-year-old article in SCIENTIFIC AMERICAN
> on fitting a pendulum clock with a crystal-controlled device that tweaks
> the pendulum period to make the clock super accurate. The author doesn't
> use an oven; he uses a "tuning capacitance" that has a special tempco,

And is totally impossible to get.

> along with a selected 3 mHz crystal. Is anyone familiar with this article?

No, but I can tell you that the guy had access to an astronomical
precision timebase offhand, from how he specs his error. He also does not
say how many hours he spent tweaking the compensation. It would be nice to
know more details though, there may be something to it. My hunch: He used
the differential error of the crystal and pendulum. Other hunch: he did
not compensate for gravity variation induced pendulum problems.

Peter