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10 inch Slide Rule vs. Pocket Calculator
From: Greg Rudzinski
Date: 2009 May 27, 19:01 -0700

```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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