# NavList:

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

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Re: 10 inch Slide Rule vs. Pocket Calculator
From: Greg Rudzinski
Date: 2009 May 28, 19:20 -0700

```A more favorable low altitude sight reduction simulation for the 10"
K&E 4080-3 slide rule.

Given:
Declination 20 South, Latitude 35 North, Meridian Angle 50

K&E 4080-3 unassisted
.495 - .1962 = .2988   INV SIN = 17� 23' (0.55' high)

K&E 4080-3 assisted by Bowditch table #31 for INV SIN
.2988   INV SIN = 17� 23.5' (1.05' high)

Trig 9 Digit Calculation:
.494786489 - .196174695 = .298611794  INV SIN = 17� 22.4546'

Trig 3 Digit Calculation:
.495 - .196 = .299  INV SIN = 17� 23.9' (1.45' high)

Trig 4 Digit Calculation:
.4948 - .1962 = .2986 INV SIN = 17� 22.41' (.04' low)

Conclusion: For low altitude sight reductions the 10" K&E 4080-3 works
well without the need for a Bowditch table #31 INV SIN reference and
seems to out perform a three digit trig calculator calculation.

On May 27, 7:01�pm, Greg Rudzinski  wrote:
> The following is a simulated slide rule vs. pocket calculator altitude
> sight reduction comparison for declination 20 degrees north, meridian
> angle 25 degrees, and latitude 15 degrees north. A 10 inch �K & E
> 4080-3 was used for slide calculations. A hp 9s scientific calculator
> was used for 9 digit comparison.
>
> Formula: Calculated Altitude = COSdec COSlat COSmeridian angle +/- SIN
> dec SIN lat
>
> The slide rule method uses Bowditch table #31 for inverse SIN. A
> magnifying glass x2 was used to improve scale resolution:
> (calculation time 3 minutes)
>
> .822 + .0885 = .9105 � �inverse SIN .9105 = 65� 35.0' �(4.9' low)
>
> Trig pocket calculator calculation to 9 digits:
> (calculation time 90 seconds)
>
> .822631444 + .088521326 = .911152770 � inverse SIN .911152770 = 65�
> 39.91'
>
> Trig pocket calculator to 3 digits:
>
> .823 + .089 = .912 � inverse SIN .912 = 65� 47.0' (7.1' high)
>
> Preliminary Conclusion: A slide rule with magnifying glass is equal to
> 3 digit accuracy if Bowditch table #31 is used for inverse SIN.
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