Time Variables - to make the PGS system more consistent with LBNL's other data streams,
the variable 'yyyymmddhhmmss' was renamed 'yyyydddhhmmss'. Also, at the bottom of each
file, variables 'yyyy','mon','hour','min' were added for those users who prefer to use these
variables instead. The new 'time' variable (seconds since midnight of the start of file)
was added to make files compatible with the new recommendations.
Quality Control Flags - to prevent confusion, the quality control flags 'qc_co2ppm' and
'qc_sum_co2' were combined. The flag 'qc_sum_co2' was elliminated and 'qc_co2ppm' now
performs range checking on 'co2ppm' variable as well as checking values of all dependencies'