The LEP Energy Working Group (or LEP ECAL group) was established
at the beginning of the LEP programme with the task of determining
the collision energies.
The group consisted of physicists from the experiments,
and machine physicists and engineers from the accelerator.
The primary purposes of the work was to provide
input to the Z mass and width measurements, and the W mass determination.
The conclusions of this work can be found in the LEP 1 (Eur. Phys. J. C 6, 187-223 (1999) ) and
LEP 2
(Eur. Phys. J. C 39, 253-292 (2005) ) ECAL publications.