The Swiss Ephemeris is based upon the latest planetary and lunar ephemeris, DE405/406, developed by NASA's Jet Propulsion Laboratory.
The timespan of the JPL ephemeris has been extended by numerical integration, so that Swiss Ephemeris covers the years 5400 BC to 5400 AD, a total of 10800 years. For this extended timespan the ephemeris requires 32 Mbytes of ephemeris files.
All transformation steps from the inertial timeframe of the JPL DE406 integration to the reference frame for astrological coordinates (true equinox of date), all corrections like relativistic aberration, deflection of light in the gravity field of the Sun etc. have been performed with utmost care and precision so that the target precision of 0.001 arcsec is maintained through all transformation steps. Never before has such a high precision ephemeris been available to astrologers.
In addition to the astronomical planets as contained in the JPL integration, we have included all other bodies and hypothetical factors which are of interest to the astrologer. We have used our own numerical integration program to provide ephemerides for ALL known asteroids.
Speed: The Swiss Ephemeris is precise and fast. On our Linux test machine, a 1000 MHz Pentium III, we compute 10'000 complete sets of planetary positions, i.e. 10'000 x 11 planets, in 9 seconds. This is 0.9 milliseconds for the complete set of exact planetary positions (consecutive 1 day steps).