# 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: Gary LaPook
Date: 2009 May 28, 02:48 -0700

```I decided to give this problem a try on several devices.

On the MB-2A circular flight computer I got 66�.

Using Dave Walden's ARG1 scale I got 66� 30'.

Using a K&E 4080-3 and the sine-cosine formula I got 65� 48'.

Using the K&E 4080-3 and the Bygrave method I got 65� 40'.

Using the flat Bygrave I got 65� 41'.

H.O. 229 gives the answer as 65� 39.9'.

Using the Bygrave method on the 10 inch rule is definitely better than
using the sine-cosine formulas.

gl

On May 27, 7:42�pm, Hewitt Schlereth  wrote:
> That's neat, Greg, especially since the cosine part is all at the
> right end of the scale. I did it with a 10" rule w/o magnifier (under
> strong light) and got Hc=65�35' , reading right off the rule. -Hewitt
>
> On 5/27/09, 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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