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I also purchased a unit similar to the Warren-Knight version in your first 
image.  It isn't near me, so I can not  check to see who manufactured it 
but I know it was made for a the US Navy (BuShips).  A very impressive 
instrument.

I have often wondered why the instrument needed to be so accurate, My 
old unit has verniers that permit measurements to 1'.  Better sextants will 
do about 10".  What does this phenomenal instrument accuracy translate 
to when working with a real chart?  Even using the finest width pencils 
available today (they weren't around in WWII) how can you really plot 
angular data to 1'.

Of course today this is done mathematically and such wondrous devices 
are no longer really needed, right?  Any clue what these cost today, new 
from factory?

Frank J.
Rochester, NY   

Date sent:          Sat, 17 Mar 2007 09:49:14 +0100
From:               Nicol�s de Hilster 
Subject:            [NavList 2391] Re: Coastal Plotting Sheets
To:                 NavList@fer3.com
Send reply to:      NavList@fer3.com

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P F wrote:
> What this coastal nav course proposed was taking the same three
> corrected bearings but plotting from the fix position onto clear
> material from a point on the plastic sheet representing the side
> opposite to the land � the seaward side. So three position lines
> radiating outwards.
>
> Then placing this clear sheet upon the chart and adjusting it until
> all three position lines are placed over the features they point
> towards � and beyond. You can immediately see the advantage � there
> is no ambiguity about the fix as the triangle proposes; the fix is a
> point.
For this purpose a nice instrument was constructed: the protractor or
"station pointer". The station pointer consists of a divided circle
with three legs and was used mainly for sextant observations using
beacons on shore. The legs could be adjusted by either a vernier or
drum micrometer. The two measured angles (or reduced bearings as in
this case) could be set on this instrument, after which the whole
instrument could be placed on top of a chart of the area. After moving
the instrument around until the three legs crossed the beacons on the
map the middle the station pointer would then be your position.

Examples of the instrument can be found on my web-site:
http://www.dehilster.info/instrumenten/stationpointer1/index.html
http://www.dehilster.info/instrumenten/stationpointer2/index.html

The first one comes with a whole range of plotting aids like a 
push-button pin and a cross-hair with pencil hole. The second one
simply has a ruler in the centre with a small notch in it.

Nicol�s




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