Table 2: Comparison of the FITS coordinate keywords in the old and new system, for helioprojective-cartesian coordinates in the TAN projection. The phrase "exactly the same'' assumes that the same units are used in both cases. See Sect. 9.2 for a discussion of angular units. Although CUNITi did not appear in the original Wells et al. (1981) paper, it has been commonly used.

Keyword	Original	WCS
CRPIXj	Exactly the same in both systems
CRVALi	Exactly the same in both systems
CDELTi	Exactly the same in both systems
CROTAi	Rotation angle	Deprecated
PCi_j	Not used	Replaces CROTAi
CUNITi	Exactly the same in both systems
CTYPEi	SOLARX	HPLN-TAN
	SOLARY	HPLT-TAN