If a Label value has not been set for a Frame axis, then a suitable default is supplied, depending on whether or not the Frame is a SkyFrame.
The default for simple Frames is the string "Axis <n>", where < > is 1, 2, etc. for each successive axis.
The default labels for specialised Frames (SkyFrames, SpecFrames, etc.) depend on the particular co-ordinate system represented by the Frame (e.g. "Right ascension", "Galactic latitude", "Frequency", "Wavelength in air", etc.).
KAPPA --- Kernel Application Package