This file contains extinction data as determined by the CARLSBERG MERIDIAN TELESCOPE (CMT) on the island of La Palma in the Canary Islands. The nightly values are derived from CCD frames in the SDSS r' band. Each frame contains an average of 30 - 40 photometric standard stars. Explanation of data columns: (1) Evening date ie. date before midnight. (2) Version number of data. If 0 then unchecked. (3) Extinction in r'. This is the median value of the extinction from all photometric frames. : indicates an uncertain value due to the night probably not being photometric. (4) Standard error on (3) = Scatter/sqrt(N_frames) (5) Scatter (robust estimate of the Gaussian sigma based on percentiles of the distribution). If this value is high (0.060), then the night was probably not photometric. (6) Number of photometric frames (7) Number of hours of photometric data taken. (8) Number of hours of non-photometric data taken. (9) Comment Evening Ext Error Scat Nf Phot Non-Phot Comment Date r' (1) (2) (3) (4) (5) (6) (7) (8) (9)