It is also a high-quality spherical astronomy text with many references to the current research literature. Note that it contains very few worked examples and the math is much more advanced than in Meeus. Some of the chapters deal with issues of the professional astronomer that will not usually concern the amateur. Ocean tidal pressure on the continental shelves, and atmospheric pressure above the continents, can cause elevation to vary by similar amounts. Note also that they use a different method of calculating planetary positions than does Meeus.
Astronomy publishes programs from time to time.
This is no longer published. Pseudo-code articles would be of greater use to those trying to understand the calculations. There are astronomical amounts of data online. I have not been paying attention to announcements of these programs in sci.astro.amateur . The same site carries many other ephemeris programs also for other platforms.