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At 10:26 AM 10/7/04 -0500, you wrote:
>Michael,
>Thank you for your message.
>I am trying to imagine how a "mechanical averaging"
>device could possibly work, on what principle.
>Can this be explained in few lines?

Here's what the manual says....

The actual averaging is accomplished by three rotatable units, each
revolving in the same adjacent parallel planes; the indexing arm assembly,
positioned by the micrometer scale drum; the averaging disc assembly,
driven 60 revolutions in approximately two minutes by the movement of the
clockworks; and the averaging gear, which actuates the counter.  As the
averaging disc rotates, the averaging pawl mounted on its outer edge is
tripped by means of a pin on the indexing arm (mechanically representing
the sighted angle) and engages the toothed circumference of the averaging
gear.  The averaging disc and the averaging gear then rotate simultaneously
until the averaging pawl is again tripped by the pawl lift pin
(mechanically representing the base line), and at that point disengaged
from the averaging gear.  The motion of the averaging gear during the time
it is engaged, represents one sixtieth of the difference between the
sighted angle and the chosen base line angle.  Thus by the adding of one
-sixtieth of each of 60 separate angles in the recording counter, the final
angle indicated on the counter will be the average of 60 sights made during
the two minutes of observation.

Actually, it's accomplished with much whirring :-).

Form the operators perspective.

You clear the counter and set  some levers to an initial state
You take a preliminary observation to get things about in the right place.
You press lever 2 and rotate the drum down (changing the observation angle)
until it reaches a stop.  This established the base line with the drum
micrometer
    set to some multiple of 10 degrees exactly.
You again obtain coincidence, and press lever three, this starts the
averaging device, lots of whirring.

The counter consists of two wheels, one is marked from 0 - 60 although it
does not appear to be a digital counter so it can do variable size
steps.The other goes from 0 - 9 and operates in a digital manner.

If you watch the counter during operation, you will see....

The counter incremented 60 times.

If the drum is set to the base line, the counter does not move.  It moves
faster as you increase from the base line.

If the drum is set 10 minutes above the baseline, you see the counter do
very small steps with the counter reading 0-10 at the end.

If the drum is set 25 minutes above the baseline, you see the counter do
bigger steps and read 0-25 at the end.

If the drum is set 1degree 30 minutes above the baseline, the counter reads
1-30 at the end.

The smallest division on the drum and hence the precision of the instrument
is 2 minutes although one could easily estimate 1 minute..  I set the drum
4 minute above the baseline, at the end the counter had crept ahead to 0-2.

>Alex.

   

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