Calibration of centre-of-mass energies at LEP 2 for a precise measurement of the W boson mass by Assmann, R, Soto, E, Cornuet, D, Dehning, B, Hildreth, M, Matheson, J, Mugnai, G, Muller, A, Peschardt, E, Placidi, M, Prochnow, J, Roncarolo, F, Renton, P, Torrence, E, Wells, P, Wenninger, J, Wilkinson, G, Grp, L