 Mounted behind the plate is a star-planisphere, based on a north pole stereographic zenithal projection (a projection from the north pole onto a plane passing through the south pole and perpendicular to the solar axis).This rotates once in a sidereal day on an axis passing through its south celestial pole and located some 13 cm above the centre of the horizon plate.For decoration it carries a few basic star patterns (considerably distorted owing to the projection used) and an eccentric zodiac/ecliptic/calendar ring faced with silver, and restricted in width to the distance between the solstitial points.