Swiss Ephemeris

Swiss Ephemeris is a high-precision astronomical calculation library developed by Astrodienst (the team behind Astro.com). It is built on NASA's JPL DE431 planetary data and is widely considered the gold standard for astrological computation. Swiss Ephemeris handles planet positions, house cusps, fixed stars, asteroids, and sidereal zodiacs with sub-arc-second accuracy from 13201 BCE through 17191 CE. Major professional tools—Solar Fire, Jagannatha Hora, TimePassages, and Astro.com itself—rely on Swiss Ephemeris or its equivalent. The library is free for non-commercial use and commercially licensed for professional astrology applications.

Your chart positions are as accurate as the best-paid professional astrology software in the world. If you compare your TriAstra chart to one drawn by a professional astrologer using Solar Fire or Astro.com, the numbers will match to the arc-second.