# NavList:

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

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Re: Geeks [slide] rule!
Date: 2013 Mar 26, 22:02 -0400

Hi Sean

Here's how to do arcsin, arccos and arctan.

Let's assume you want the arcsin(.43).  Set your cursor on the D scale to 430.  Read on the S (sin) scale the value 26 degrees.

Let's assume you want the arctan(.707).  Set your cursor on the D scale to 707 (okay 710).  Read on the T scale 35 degrees

Lets assume you want the arccos(.350).  Set your cursor on 350 on the D scale.  Flip the scale over and read on the S scale 21.  Cos(angle)=Sin(angle-90), so your answer is (90-21=) 69 degrees.

These answers are not exact but show the method.  You can do better with more careful manipulation of the cursor.

Regards

On Mar 26, 2013 8:32 PM, "Sean C" <yhshuh---.com> wrote:

I purchased a Pickett model N902-ES "slipstick" from eBay. I remember having a slide rule around the house when I was a kid, but this has been my first 'real' experience with one. (Not counting the flat Bygrave.)

I am enjoying learning how to use it immensely. Seriously, this thing is way handy. I just tried running through the formulae for determining a DR from the N.A. (L1=Lf+t(v/60)sin(T)/cos(Bf), etc.) My results were remarkably accurate!

I'm now one step closer to surviving the E.M.P. apocalypse. :P

P.S.
Is there any way to figure arcsin/arccos on the average slide rule. Or is that why Capt. Bygrave invented his rule?

-Sean C.
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