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I think the question is not how sharp you can sharpen
a pencil, or a needle (the "protractor" uses a needle to make
a mark on the map) but whether you really can make a better use
of a 0.2mm dot on the map as compared with 0.5 mm dot:-)
besides, the 2 feet arms of this "protractor" certainly cannot have enough
rigidity to plot with 0.2mm accuracy, though they seem to be made
of the same bronze as the sextant frames, and the designer took all
precautions to make the joints inflexible.
(The arms consist of two pieces, so that the main part 1 ft long can be
extended to 2 ft, but the whole thing packs in a box slightly more
that 1 ft).

The device was known in the English-speaking world in XIX century
under the name "station pointer". It is shown on p. 137 of Lecky's
Wrinkles, with verniers but no magnifying glass.

Russians and Japanese were apparently more conservative, and made
this well into XX century, as well as the star globe instead
of a simple star finder.


Alex

On Sat, 31 Mar 2012, Greg Rudzinski wrote:

>
> Bill,
>
> 0.7mm is a good compromise width. Won't break as easy as the 0.5mm and 0.3mm 
yet fine enough for most navigating needs.
>
>
> [NavList] Re: Current Sextant Manufacturers
> From: Bill B
> Date: 31 Mar 2012 16:16
> On 3/31/2012 2:09 PM, Greg Rudzinski wrote:
>> Alex,
>>
>> Some mechanical pencils have 0.5mm leads
>>
> Also 0.3mm
>
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