When you now select sidereal zodiac option, there are several new Ayanamsha options to choose from.
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