Due to various errors like misalignment errors, field errors, fringe fields etc., the closed orbit does not coincide with the reference orbit. The closed orbit also changes with the momentum error. The closed orbit is described with respect to the reference orbit, using the local reference system (x, y, s). It is evaluated including any nonlinear effects.

computes the betatron and synchrotron oscillations with respect to the closed orbit. Results are given in the local (x, y, s)-system defined by the reference orbit.