Hi, I agree with Patrick's comments about James Miller's PLAN13 tracking program. I have been using it for all my tracking since about 1985! The original code is in BBC BASIC which runs on a BBC Micro computer, which was popular in the UK during the last decade. However the code is exceptionally well documented, and may be converted to other dialects of BASIC, or other languages such as C or Pascal. The original program is file a110.zip in the AMSAT FTP site - ftp://ftp.amsat.org/amsat/articles/g3ruh/ It is also included it in a package on my own website. The package is for evaluating solar eclipses, and runs in QBASIC. Although this is a specialised application of the PLAN13 program, much of the original code has been converted to QBASIC, and it would be fairly easy to expand the routines into a general tracking program. I intend to do this sometime! The package also includes a small BBC BASIC interpreter, which enables the original code to be run on a PC. The URL is www.users.zetnet.co.uk/clivew/ The package is SATILL.ZIP, and it's in the GENERAL SATELLITE page. -- 73 Clive G3CWV Hitchin, North Hertfordshire, UK.