# NavList:

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

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
From: Greg Rudzinski
Date: 2018 Oct 31, 09:00 -0700

Alex.

A 6" slide rule is good enough for almost all navigation needs except for calculated altitude Hc , time sight local hour angle LHA, and great circle distance ZD (zenith distance).

I use the 6" for time speed distance, azimuth, prime vertical, ex-meridian, amplitude, interpolation, horizontal sextant angle circle of position radius, vertical distance off, dip, refraction, and appx Hc pre calculation.

For Hc. ,time sight, and great circle distance slide rule calculations I like using the Ottis King with 1' trig tables.

Greg RudzinskiFrom: Alexander Duytschaever
Date: 2018 Oct 26, 06:38 -0700

Hello,

I'm a n00b user/amateur astronav that dived into astro navigation after stumbling over a Bris sextant and wondering if one could ever perform LOP calculatons using a slide rule (got a few of those) :-) (*) So I soon acquired a small shiny King Hughes 1917 replica and recently a Davis Mk 15, and I can happily live with their shortcomings (found an article on how to deal with those shortcomings, and I still have to calibrate these three).

My question is: what is the logic behind the different shades? I understand that one needs more shades for the index mirror (4 vs 3 for the horizon), but why were those colours (blue, blue, orange, grey) chosen? I suspect that the light grey colour can be used for moderate lighting or to increase contrast, and it also reminds of lunar light conditions; but the two blue glasses look similar (I guess a main function is to block out UV), but are there intended ways to combine those glasses?

thx

-alex-

(*) for now, my answer is that a SR can serve for interpolations; it doesn't have enough digits to provide sufficient accuracy. or maybe with A LOT of sightings, who knows...

Browse Files

Drop Files

### Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

### Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

### Email Settings

 Posting Code:

### Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)