D. Walker (dwalker@ldeo.columbia.edu), S.M. Clark(*) (s.m.clark@dl.ac.uk), R.L. Jones(*) (r.l.jones@dl.ac.uk) and L.M.D. Cranswick(*) (l.cranswick@dl.ac.uk) Lamont Doherty Earth Observatory, Columbia University, Palisades, NY 10964 USA. * CLRC, Daresbury Laboratory, Warrington, WA4 4AD, UK. Deposited at http://www.ccp14.ac.uk/projects/glass-calib/