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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Sextant averager
From: Gary LaPook
Date: 2010 Oct 12, 13:03 -0700

```  ﻿It took me a while to figure out how this averager works. At first I
thought it was as described
at:
http://fer3.com/arc/m2.aspx?i=018062&y=200410

that it was simply and integrator that multiplied the displacement from
the starting altitude
by the time. But when I took one apart I was surprised to find that the
time element was supplied
by the ball moving across the disk and not by the rotation of the disk
which actually supplies the
altitude component.

I finally figured it out, it is all in the last movement, turning the
altitude knob back after the shot.
I reasoned it out this way which might help in your understanding of
this device, refer to figure
20 in the patent document at:

http://www.fer3.com/arc/imgx/MA-2-Manual.pdf

These examples should help. Starting with the altitude set to 30 degrees
you start the averager and then
immediately change the altitude to 40 degrees where it stays until the
end of the averaging
period, two minutes. Since, at the beginning the ball is located in the
center of the disk that
rotates when you turn the altitude knob, changing the altitude transmits
no motion to the drum so
the drum index dial doesn’t move. So when it comes to the point to
rotate the altitude knob to
move the drum index dial back to zero, no change is required and you
read out the average as the
final altitude, 40 degrees which is obvious since it stayed at this
value for the whole period.

Second example. Starting again at 30 degrees you start the averager
running. Just before the end
of the averaging period you rotate the altitude knob to 40 degrees and
then the averager stops.
When the altitude knob was turned the ball had reached the edge of the
disk so it moved the
drum the maximum amount possible and the drum index dial moved the
maximum amount also.
Now, when you rotate the altitude knob to move the drum index dial back
to zero, it will move
exactly the same amount as it moved when the altitude was changed from
30 degrees to 40
which makes sense since
it stayed at this value for the entire shooting period.

Third example. Again starting at 30 degrees you start the averager
running and at the one minute
point you change the altitude to 40 degrees where it remains to the end
of the shooting period. At
the one minute point the ball had moved only half way to the edge of the
disk so when the
altitude was changed to 40 degrees the drum index dial only moves half
as far as it did in the
second example. After the shot, when the altitude knob is rotated to
move the drum index dial
back to zero, the ball has reached the edge of the disk so the drum
moves twice as fast as it did
when the knob was rotated to change the altitude from 30 to 40 degrees.
So now rotating the
knob back towards 30 degrees the drum index dial reaches the zero
position when the altitude
readout has only gone back as far as 35 degrees which is the average.

In the more normal case when there are variations in the altitudes
during the shooting period the
operation of moving the drum index dial back to zero moves the altitude
average of all the positions taken by the altitude readout during the
two minute period.

gl

On 10/10/2010 5:43 PM, Gary LaPook wrote:
> Here is the patent on the Dreimel-Black averager used in the Kollsman
> sextant. The patent used an A-10 sextant to illustrate the invention.
>
> Also see:
>
> http://www.fer3.com/arc/imgx/MA-2-Manual.pdf
>
>
> The following post describes the operation of the averager but has it
> wrong since the ball moves from the center to the edge of the rotating
> disk at a constant rate driven by clockwork and the rotating disk is
> turned by the altitude knob which is exactly the opposite of this
> description.
>
>
> http://fer3.com/arc/m2.aspx?i=018062&y=200410
>
>
>
> gl

```
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