Table 1: Spectral coordinate type codes, (characters 1-4 of CTYPE $k{\it a\/}$).
Code Name Symbol Associate Default
      variable units
FREQ Frequency $\nu$ $\nu$ Hz
ENER Energy E $\nu$ J
WAVN Wavenumber $\kappa$ $\nu$ m-1
VRAD Radio velocity V $\nu$ m  s-1
WAVE Vacuum wavelength $\lambda$ $\lambda$ m
VOPT Optical velocity Z $\lambda$ m  s-1
ZOPT Redshift z $\lambda$ -
AWAV Air wavelength $\lambda_{\rm a}$ $\lambda_{\rm a}$ m
VELO Apparent radial velocity $\varv$ $\varv$ m  s-1
BETA Beta factor ($\varv /c$) $\beta$ $\varv$ -


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