Oops. Forgot to fix up headers.

Olin Lathrop <olin_piclist@EMBEDINC.COM> wrote:
> > Why? Pendulum clocks (same basic technology) are at least an order of
> > magnitude more accurate than that (1 min/day or better).
>
> Because the simple metronomes I was referring to were far from pendulum
> clocks.  The ones I remember had an inverted pendulum (pivot at the
> bottom).  A spring provided just enough force to keep the pendulum
> straight up against gravity.  A normal clock mechanism would cause the
> pendulum to oscillate.  A weight with a spring clip was slid up and down
> the pendulum to adjust the speed.  Higher weight position increased length
> from pivot to center of mass, which reduced the tick rate.  The pendulum
> was marked with a beats/minute scale so you knew where to set the weight.
> The whole thing was powered by a windup spring, like a windup clock.
>
> I seriously doubt that the spring alone was guaranteed within 1%.
> Additional manufacturing variations in the weight, marking of the pendulum
> scale, effect of windup tension, etc, very likely exceeded 1% too.

Here's a picture that shows more of the mechanism:
   http://www.musiclink.co.uk/metronomes/884r.jpg

As with any spring-driven clock, the mainspring force has very little if
anything to do with the basic regulation; it works through an escapement
mechanism to provide a tiny periodic kick that overcomes the frictional
losses.

The arm with its two weights is more analagous to the balance wheel in a
wristwatch; the regulation is accomplished by balancing the restoring force
of its spring (not the mainspring) against the moment arm of the swinging
arm, which is varied by moving one of the weights. This could be calibrated
quite accurately.

> My original point was that nobody at the time complained about the
> accuracy of these things.  It just didn't matter whether you practised
> a piece at 100 beats/minute or 101 beats/minute.

It *does* make a difference to a musician; my point was that these devices
are more accurate than you are guesstimating.

I never owned one of these; my own first metronome was an electric one
similar to this:
   http://sj.znet.com/~regina_r/metronome.htm

-- Dave Tweed

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics