"John R. Copeland" wrote in message
...

"Robert Moore" wrote in message
. 6...
"Maule Driver" wrote
That's glider stuff. You tap it instead of allowing engine vibration to
do it.

In the B-707, the altimeter had a built-in altimeter-tapper at about
two cps. This was required equipment in the event that the electronic
altimeter correction failed or was turned off. Turning the correction
off, turned on the tapper.

Bob Moore

The drum-and-pointer altimeter in my C340 has an internal vibrator.
I don't know its frequency, but it's much higher than 2 cps.
When it's not vibrating, there's a big hang-up every 1000 feet,
at the point where the drum reading indexes to its next value.
Engine vibration is insufficient to keep it free.
---JRC---

Us old-timers got to see the 'system' evolve from a knuckle rap
to an external strap on vibrator and eventually the built in. :-)
Looking at a 777 diagram, it seems to have AnalogDigitalModules
located right at the pitot tubes or static port pairs and no need to
rap or vibrate anything. Ain't modern technology wonderful?

JK