# NavList:

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

**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 Schlerethwrote: > 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. > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavList-unsubscribe@fer3.com -~----------~----~----~----~------~----~------~--~---