NavList:

   

Reply

I once had a circular slide rule that was an aluminum disk about 8,5
inches in diameter. It wasn't specifically for celestial; just C, D,
Sin/Cos and Tan scales. As I recall the scales were on in a spiral
which made them many feet long. I used to use it now and then to work
the fundamental sin-cos formulas for Hc and Z. I believe it was called
a Pickett 'Atlas'.

-Hewitt

On 9/19/08, d walden  wrote:
>
> Poor's "Line of Position Computer"
>
> Poor's "Line of Position Computer" is mentioned in Bowditch.  It had a
> diameter of about 15 inches.  A question was raised once in the group, but I
> couldn't find any follow up.  It would seem, few were made.  I haven't seen
> one available.  Finding no other real circular slide rule type methods
> (that's circular not cylindrical, which has been discussed on list), I
> decided to build one myself.  Details of the computer can be found in:
>
> Simplified Navigation for Ships and Aircraft    By Charles Lane Poor
> http://books.google.com/books?id=KPg3AAAAMAAJ&printsec=titlepage
>
> Unfortunately, in the Google books version, the fold outs don't.  I found a
> hard copy quite cheap online.
>
> Several possibilities for making one presented themselves:
>
> 1 Print out two halves from google pdf and paste together.
> pros: cheap, anyone can do it, easy, little investment of time or money
> cons: pdf scans are low resolution, hard to read, and enlarging makes things
> worse
>
> 2 Copy from book and blow up.
> pros: have entire fold out, high resolution scans possible, enlarging is
> better
> cons: need the book
>
> 3 Create from scratch using postscript.
> pros: can customize, can print high res at any size, can learn how scales
> are made
> cons: have to create postscript file
>
> Well, I tried all three.  Number one is quick and easy, but the result in
> not very satisfactory.  Two is better,  but Hour Angles are in hours using
> Roman Numerals and style is very much early twentieth century (not that
> that's necessarily all bad!)  So, I went for three.  I wrote a FORTRAN
> program to generate the postscript file making it easy to make changes and
> quickly iterate and see the results.
>
> Attached is a 8 1/2 x 11 inch pdf of the result.  At this size, index marks
> are no less than one degree.  It's still a work in progress, so any comments
> or questions are welcome.  The postscript file and FORTRAN source are
> available.  I made the circle and arm using transparency film and used a
> paper clip as a clamp.
>
> Some hints: it's easier in practice than it seems from reading the book,
> some scales increase CW, some CCW; be careful,  a quick "cheat sheet":
>
> Poor's LOP Computer
> To find alt
> set circle at dec
> clamp arm at lat
> move circle to t
> read arm is number on 3a is 2a/1, 2b/10 ,2c/100 & NOTE
> set circle at 0
> clamp arm at zd scale=L~D=abs(signed difference)
> move circle to number on 3b
> read arm is alt
>
> To find z
> set circle at t
> clamp arm at alt
> move arm to dec
> read circle is z
>
>
> NOTE:
> if  dec to lat less than 60 deg
> and circle left of 0.0
> and arm right of lat 60 deg
>  and t is on 2b
>  then number is 2b/1
>  or
>  and t is on 2c
>  then number is 2c/10
>
> if  dec to lat greater than 60 deg
> and circle right of 0.0
> and arm left of lat 60 deg
> then number is number/10
>
>
>  >
>

--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply