# NavList:

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

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Re: Calculator v. Slide Rule for Ex-Meridian Correction
From: Hewitt Schlereth
Date: 2016 Jan 3, 14:43 -0800
Speaking of books in this context, my favorite is HH Shufeldt's Slide Rule for the Mariner. I got it in 1972 and it was my introduction to the fundamental cel nav formulas. According to him it was a standard tool for air navigators in the Pacific during WW II.

Hewitt

On Jan 3, 2016, at 1:49 PM, Rommel John Miller <NoReply_Miller@fer3.com> wrote:

Here we go two of my favorite books are Neville W. Young  and A Complete Slide Rule Manual and J. C. Podmore's The Slide Rule For Sea and Air Navigation.

Young on page 1-3 in exercise 1(a) question v (five) asks the reader to find 0.04125 on a very elementary.       ( with one log scale) the other scales are C„ D„ CI, DI,  CF and DF as well CIF and of course L.

Pod more uses the Trig version of the Academy Duplex 504 made by Blundell an English Company and he has readers on page 16 consider the characteristic of property +4 .  Example given is 0.0034*0.125*4.8*.37500  a calculator gives us 0.000765 as the product.  Pod more tells us that the true answer is 76.5 and why?  Since a slide only gives a answer to tertiary graduation.  Knowing the product infers the characteristic property of +4.  All of which is done on the C and D scales and very elementary math.

Pod more does address the trig scales in Chapter 4.

I hope this clears up the doubt of anyone that only three digits are possible.  One has to be intelligent enough to infer a correct answer before begining to use the slide rule. Therefore infinite places are available using a slide rule how else could Apollo 13 gotten back to earth without the leading slide rule of the day?

Buzz Aldrin loves to encorse the slide rule and boasts the 6in Pickett N-600 went to the moon and back in his pen pocket.

Von Braun got the Apollo rockets into space (and developed the V-2 for the Nazi's with a slide rule and paper and pencil)

Frank Lloyd Wright designed great structures with the help of the key calculating device of his time.

So please don't disparage the limits of a slide rule.  It is an insult to those of us who still use them as a backup to cloudy days and solar or dead batteries.

Both the sextant and slide rule do not require batteries.  Quartz chronometers and calculators do.

The navy finally wised up and realized satellites are vulnerable too.

Wind sail a good compass sextant and slide are my answer to failing tecknology today.

My two cents.

Rommel John Miller
sent from my smart phone

On Jan 3, 2016 3:17 PM, "Frank Reed" <NoReply_FrankReed@fer3.com> wrote:

The method Letcher describes for clearing lunars is a simple, efficient variant of the standard series method. Of course, I have pointed this out many times over the years. You can read a basic version of it in my Easy Lunars essay (originally posted for NavList way back in 2004). The series method requires only three significant figures anc can easily be worked on a slide rule (if one is compelled to apply an obsolete technology in a fashion which was never employed historically). You may also get something from my post on the math of clearing lunars which I wrote up for NavList last June.

Frank Reed

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