Sidereal zodiac
Signs measured against the stars rather than the seasons. The two zodiacs drift apart by about a degree every 72 years; today the gap, the ayanamsa, is near 24 degrees.
The tropical zodiac starts Aries at the March equinox. The sidereal zodiac pins the signs to the constellations instead. Because the equinox slides slowly backward against the stars, the two zodiacs drift apart, by roughly one degree every 72 years.
The offset between them is the ayanamsa, and schools disagree on where to anchor it. Aspicio offers four: Lahiri, the Indian government standard; Fagan-Bradley, used by Western siderealists; Krishnamurti; and Raman. They differ by a little over two degrees at most (Fagan-Bradley and Raman), and each chart names the one it used.
Choosing sidereal shifts every position, angle and cusp by the ayanamsa. The written readings on the site were composed for the tropical zodiac, so they stay tropical and say so when sidereal is on.