* The index error is regarded as positive when the angle
displayed by the instrument is greater than the actual angle.
The internal almanac is based upon formulas given in
Astronomical Algorithms by Jean Meeus, and is valid through
approx. 2040 (cross-checked with Interactive Computer Ephemeris
0.51 by USNO). The almanac is usually accurate to 0.03'. Beyond
2010, the accuracy will probably slowly decrease but still
remain better than 0.1' (comparable to the Nautical Almanac).
The program internally sets dip=0 if any form of an artificial
horizon or a zenith distance is chosen. If an external
artificial horizon (pan with liquid) is used, the sextant
altitude is automatically divided by two after subtracting the
index error. This program is free software: you can redistribute
it and/or modify it under the terms of the GNU General Public
License as published by the Free Software Foundation, either
version 3 of the license or any later version. This program is
distributed in the hope that it will be useful, but W