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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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