Orbit Steering and Central Frequency for LEP2 Energy Calibration

"The central frequency is an important parameter of the LEP beam energy model. It is a direct measurementof the LEP circumference and is used to evaluate the contribution of the quadrupoles to field integral relevant forthe LEP beam ebergy. Its evolution over a run is tracked using direct frequency measurementscombined with radial beam position measurements in the LEP arcs.The influence of orbit corrections on the central frequency measurement techniques was evaluatedand a model allowing to correct for changes of corrector settings was developped.The central frequency data for the LEP2 runs between 1996 and 1999 was re-analysed to includecorrections due to the closed orbit steering."