# Pub. 249 vs Pub. 229: which tables to use?

Pub. 249 and Pub. 229 are the two families of sight reduction tables. Both give the computed altitude (Hc) and azimuth of a body for a latitude, hour angle and declination. They differ in precision, coverage and bulk.

## Pub. 249

Written for air navigators and widely adopted by small-boat sailors. Three volumes:

- **Volume 1, selected stars.** For each latitude and LHA of Aries it lists seven well-placed stars with Hc and the true bearing Zn directly: no declination, no interpolation. It is tied to an epoch and reissued every five years.
- **Volumes 2 and 3** (latitudes 0° to 40° and 39° to 89°). For declinations from 0° to 29°, which covers the Sun, Moon and planets always, and the stars within 29° of the equator.

Hc is given to the nearest minute and the azimuth angle Z to the nearest degree. A small table (Table 5) handles the odd minutes of declination.

## Pub. 229

Written for marine navigation. Six volumes, each covering 16° of latitude (0° to 15°, 15° to 30°, and so on to 90°). It covers **every declination**, so any body can be reduced. Hc is given to a tenth of a minute and Z to a tenth of a degree, with an interpolation table, and occasionally a second small correction (the double second difference) near the zenith.

## Side by side

| Feature | Pub. 249 | Pub. 229 |
| Hc precision | 1′ | 0.1′ |
| Azimuth | 1° | 0.1° |
| Declinations | 0° to 29° (Vols. 2, 3); seven chosen stars (Vol. 1) | All |
| Volumes for the world | 3 | 6 |
| Working | Shorter | A little longer |
| Goes out of date? | Vol. 1 every five years; Vols. 2, 3 never | Never |

## Which should you use?

From the deck of a small boat, a sextant altitude is rarely good to better than a minute or two. Pub. 249's whole-minute precision is not the weak link, and its working is quicker, with fewer places to slip. Most cruising sailors carry Volumes 2 and 3 for their latitudes, and Volume 1 if they shoot stars often.

Choose Pub. 229 if you want one method for every body, including stars far from the equator, or you want the extra precision for a steady platform or for checking work.

A third way is a **calculator**: the same answer from two formulas, straight from your DR, with no tables to carry. Many navigators learn the tables first, because they show what is going on, and keep a calculator as a check.

Both tables are free to download from the U.S. National Geospatial-Intelligence Agency. The British editions are NP 303 (the same tables as Pub. 249) and NP 401 (Pub. 229).

## Try all three

In the course, the [intercept method](https://asterodos.com/m/intercept) practice lets you work the same sight with Pub. 249, Pub. 229 or a calculator and see that the line of position lands in the same place. [The real books](https://asterodos.com/books/1) shows how the pages are laid out.

## Learn it properly, free

Asterodos is a free interactive course: short lessons you can see and move, and practice that checks every step of your working.

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From Asterodos, a free interactive course in celestial navigation: https://asterodos.com/pub-249-vs-pub-229
For learning, not for navigating a vessel.