### Correction

As explained in section 3.3.2, there are usually two spectra per observation: one which is the simple average of all the dumps within the observations, one for which each individual spectra is corrected by a phase , where is the correction for atmospheric phase derived from the Water Vapor Radiometer (WVR) for antenna , prior to the averaging. For older data (before 2006), the 1mm total power data have also been used to monitor atmospheric phases (see HELP MONITOR).

STORE CORRECTION can be used to store in the observation header whether the atmospheric phase correction is valid or not. Besides the GOOD or BAD keywords, keyword AUTO is the one that is recommended to be used. It will compare the amplitude of the phase corrected or uncorrected data (with a bias toward uncorrected data) on calibrators, and then automatically decide which should be used for the science scans according to the closest in time phase calibrator correction validity.