item
code for the label. This must be an element from the following
list, or an abbreviation that uniquely identifies an element through its
first letters: "S", "C", "conductivity mS/cm",
"conductivity S/m", "T", "theta", "sigmaTheta",
"conservative temperature", "absolute salinity",
"nitrate", "nitrite", "oxygen", "oxygen
saturation", "oxygen mL/L", "oxygen umol/L", "oxygen
umol/kg", "phosphate", "silicate", "tritium",
"spice", "fluorescence", "p", "z",
"distance", "distance km", "along-track distance km",
"heading", "pitch", "roll", "u", "v",
"w", "speed", "direction", "eastward",
"northward", "depth", "elevation", "latitude",
"longitude", "frequency cph", or "spectral density
m2/cph".