A levelling apparatus for a laser level includes a base having a central axis and a sphere-shaped socket component mounted to the base. A sphere-shaped ball device is received in the socket component for relative movement with respect thereto. A retention mechanism is spaced radially outwardly from the...http://www.google.com/patents/US6249983?utm_source=gb-gplus-sharePatent US6249983 - Levelling apparatus for a laser level
