When you now select sidereal zodiac option, there are several new Ayanamsha options to choose from.
Ayanamsha
Ayanamsha is the deviation in degrees of the sidereal from the tropical zodiac at a given epoch.
Sidereal astrologers dissent from each other on the question where exactly in the firmament the sidereal zodiac should have its initial point (0° Aries). For this reason, there are several different sidereal zodiacs. These are defined by their respective ayanamshas.http://www.astro.com/astrology/in_ayanamsha_e.htm