The Pupil's Astrology, Ephemeris, Ayanamsa

CALCULATION OF THE AYANAMSA [1]
There are two systems of Astronomy in India - namely the Nirayana and the Sayana. The former traces observations of planets to a fixed Zodiac, while the latter considers the moving Zodiac commencing from the shifting, Vernal Equinox. It is certain that the greatest Hindu astrological writers referred to the fixed Zodiac for predictions. And this fact is borne out by experience.
  The increment between the beginning of the "fixed" and the "moveable" Zodiacs or the Nirayana and Sayana positions is referred to as Ayanamsa which increases about 50 1/3 seconds every year. Western Astronomy is based upon the Sayana system so that it considers the moving Zodiac commencing from the shifting Vernal Equinox as has already been said above. Thus, if we deduct this Ayanamsa from the positions of planets and cusps of the houses obtained according to the western system we will arrive at the Hindu positions.
  When exactly the two Zodiacs were in the first point is doubted by a number of astronomers and accordingly the Ayanamsa-precessional distance-varies from 19° to 23°. I do not wish to enter into explaining the complicated processes of astronomy at large which centre attention on the discussion of the exact nature of Ayanamsa but merely confine myself to giving a suitable and simple method for determining the Ayanamsa.
  First of all, cast the horoscope of birth according to the European manner and convert it into the terms of the Hindu Zodiac by the following process :-

(1): Subtract 397 from the year of bitrh (A.D.).
(2): Multiply the remainder by 50 1/3 seconds; and reduce the product into degrees, minutes and seconds.
(3): Subtract this number of degrees, minutes, and seconds from the cusps of the houses and planets' positions in the European figure of birth and the figure thus obtained will be according to the Hindu system.

Example:-

 Determine the Ayanamsa for 1912 A.D.?
  1912 - 397 = 1515 * 50 1/3 " = 76255"
      76255" = 21° 10´ 55"
This is the Ayanamsa for 1912 A.D.