# NavList:

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

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Re: Unrealistic expectations
From: G Becker
Date: 2013 Oct 7, 12:37 -0400

According to the sokkia celestial observation handbook:

“An accuracy of within 10 arc-seconds can be obtained”

“The vertical angle to the sun is usually larger than for typical survey work. This increases the importance of accurately leveling the instrument. For a vertical angle of 5 deg., a leveling error of 10 arc-seconds perpendicular to the direction pointed will result in less than 1 arc-second error in the horizontal circle reading. For a vertical angle of 45 deg., however, the error would be 10 arc-seconds…… because of this and other errors; it is recommended that observation not be made when the altitude of the sun is greater than approximately 45 deg.”

“Instrument leveling error:

dR = dL tan V

dR is the error in the horizontal circle reading (arc-seconds)

dL is the leveling error perpendicular to the direction sighted (arc-seconds)

V is the vertical angle to the point sighted”

My comments…. Double check your tripod, be positive that the tripod is securely pushed into the ground. Tighten all the tripod nuts, bolts, and fittings. Triple check your level bubbles.

-----Original Message-----
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of rgaarden
Sent: Sunday, October 06, 2013 1:13 PM
To: george@gwbeckerpls.com
Subject: [NavList] Unrealistic expectations

I bought the Multiyear Interactive Computer Almanac from Willman-Bell, calculated a series of solar positions by second, and made observations during that sequence period. I then compared my observations with the calculations. I was in error on average 4.3 seconds (time) with a SD of 8.57 seconds. The sun is moving an arc minute every 4 seconds. With my current skill set locating North within 20" is out of reach.

I am not about to argue with my own numbers. Still, it is difficult to understand how I could miss the alignment of the trailing edge of the Sun with my vertical cross hair by multiple seconds.

What is a reasonable accuracy expectation for series of solar azimuth observations?

Thank you.
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