Centrans calculated the destination coordinates of a ship that entered hyperspace, transmitted to Centrans via Holtzman Waves. Centrans prepared course corrections and updated the ship with them, as soon as it entered the next "mail drop".
Centrans calculated simultaneously the courses of all thousans of Transcom ships (about more than 12000) until Xenophon was attacked by Butlerian Jihad crusaders.
Assaults like these against Centrans and similar estamblishments, marked the end of regular interstellar trade.
- Dune Encyclopedia, entry BUTLERIAN JIHAD