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 ( $\varv /c$ ) $\beta$ $\varv$ -

**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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