# 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:**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 Rudzinskiwrote: > 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 -~----------~----~----~----~------~----~------~--~---