"Robert Moore" wrote in message =
. 6...
"Maule Driver" wrote=20
That's glider stuff. You tap it instead of allowing engine =
vibration to
do it.
=20
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.
=20
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---