# NavList:

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

**Re: Longhand Sight Reduction**

**From:**Hanno Ix

**Date:**2014 Nov 29, 21:48 -0800

thank you for your comments.

Well, the term "simple" does not necessarily imply something is simple to do.

For me it means something with a simple concept. And in that sense I believe

that formula is indeed simple.

The formula can be re-written in several ways, and Lars's is an excellent one for the

intended purpose as Greg says.

As you saw in my mail, however, I assumed the use of a slide rule, not a longhand calculation for

exactly the reasons you mentioned: division and squaring. This I did, because Greg

loves using slide rules where it

*can*be used - which is the case in finding the azimuth.I do too, and so I would always take a slide rule along - even the availability of a Bygrave,

various tables, my azimuth diagram etc. would make me leave it at home.

Regards

H

PS: I just walked along embarcadero in San Francisco where sea lions hang out as well.

Those of you who have assessed the smell of various things that cause sliding must not have been

here otherwise they would agree as to what of those substances creates the absolute epitome

of smooth sliding AND bad smell! :)

On Wed, Nov 26, 2014 at 7:31 PM, Lars Bergman <NoReply_Bergman@fer3.com> wrote:

Hanno Ix wrote "here is a simple equation for the azimuth Z".

Simple? Not for longhand calculation according to me, with multiplication, division and squaring.

A more simple formula, similar to the one used for finding altitude, is this:

N = hav(latitude - altitude)

P = hav(latitude + altitude)

Q = N + P

hav(Z) = (hav(polar distance) - N) / (1-Q)

where polar distance = 90° - declination (if lat and dec are of same name; otherwise 90° + declination).

The difficult part is the division with (1-Q), for very small values of Q this could be replaced by a multiplication with (1+Q).

Lars 59N 18E