Like my teacher, Pt. Sanjay Rath, I use true Chitrapakṣa Ayanamsha. This implies using the exact degree of Spica as the 0 degree point of Libra, and thus forming the zodiac.

Why don’t we use Lahiri Ayanamsha? Because Lahiri’s Ayanamsha was supposed to be updated to adjust for the movement of Spica/Chitra, and was not. Since then the calculation has become obsolete compared to actual star positions.

Why don’t we use Sūrya Siddhānta Ayanamsha calculations? Because they do not match with the observed/actual positions of planets and stars on the heavens. The following statement will clarify from Siddhānta Sundara:

Prior to this the Sage Vasiṣṭha adds: