# NavList:

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

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Re: Abhav sightreduction?
From: Stan K
Date: 2016 Sep 18, 23:03 -0400
Axcel,

Attached is the Abhav sight reduction form (Figure 2).  Open it with anything but Notepad (Wordpad, Word, etc.).  Also attached is a worked example (same opening issues).

Stan

-----Original Message-----
To: slk1000 <slk1000@aol.com>
Sent: Fri, Sep 16, 2016 3:39 pm
Subject: [NavList] Re: Abhav sightreduction?

Hello Dave,
Wow! Thank you for the Excel file. It's quite impressive! Were all these formulas contained in the article? Anyway, now that I have the tables, I was trying to actually do an exercise but got stuck on the next problem now. The instruction below is referring to a work form several times. Unfortunately, I don't have this workform and don't get a correct value anyway. Is there anyone who could help with this please...?  Anyone who is familiar with this method? A worked example perhaps? Dave...? Please...   :-/
I find this method impressive since it can give you both, Hc and Zn. I hope, we can revive this method...
Thanks
Axcel
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#### USING THE TABLES

Figure 2 shows a sample work form. The top half of the work form is similar to most other work forms and is self explanitory.
1. Fill in the data specified to the nearest tenth of a minute of arc and to the nearest second in time.
2. Make the necessary computations to end up with values for altitude Ho, declination D and hour angle t.
On the bottom half of the form all angular entries should be to the nearest arcmin.
1. Enter t designating it either E or W as appropriate.
2. Enter the declination and latitude in the proper spaces. If either is South enter it as a negative number.
3. Look up the numbers in the table from the appropriate column for each entry as marked on the form.
4. Add the numbers as indicated to equal an A value on the next line.
5. Using the tables find a value in the B column which corresponds to the same angle as the A value just computed. When looking up values always use the entry corresponding to the closest input value. It is not necessary to interpolate.
6. Determine the L~D which is the absolute value of the difference between L and D taking note of the signs. The only time the negative sign, if any, for L and D is used is when obtaining the difference between two numbers as L~D or L~Hc).
7. For this angle get the value from the B column in the table
8. Add this B value to the previous B value to get a third B value.
9. Now using the table in reverse go in with the B value just determined and get the angle. This angle will be the zenith distance z.
In a similar manner fill in and work out the balance of the sheet.
10. Subtract z from 90 to get Hc.
11. Enter Ho and take the difference between it and Hc to get the intercept a.
12. If Ho is greater than Hc the intercept a will be toward the azimuth direction but if Hc is greater the intercept a will be away from the the azimuth direction.
13. Go to the right hand side of the form and enter polar distance in the p space. p is 90 - D. Get the B value from the tables.
14. For L~Hc, Observe the sign get the absolute value of the difference between L and Hc. Get the B value from the tables.
15. Subtract the second B value from the first B value getting a third B value.
16. Using the tables convert this to an A value.
17. The L and C entries can be copied from the same values previously used.
18. Get a C value from the table for Hc
19. Add this to the C value just above it and enter as an s (sum) value.
20. Transfer the s value to the s- space where it will be subtracted from the A above it.
21. The result will be another A value.
22. Enter the table with this A value and come out with an angle which will be the azimuth angle Z.
23. convert Z to Zn. The azimuth angle will always have a prefix of N and a suffix to agree with the suffix for t.
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