Ayanamsa
The ayanamsa is the angle between the tropical and the sidereal zodiac, about 24 degrees today.
What it is
Ayanamsa is a Sanskrit word for the gap between the two zodiacs. It grows by about one degree every 72 years as Earth's axis precesses. Astrologers use slightly different values; the most widely used, and the official standard in India, is the Lahiri ayanamsa.
In AstroFinex
AstroFinex uses the Lahiri ayanamsa everywhere. Subtract it from a tropical position and you get the sidereal position the engine works with.