#### Description:

This attribute gives the total number of unique FITS keywords stored in a FitsChan. It is updated as cards are added or deleted. If no keyword occurrs more than once in the FitsChan, the Ncard and Nkey attributes will be equal. If any keyword occurrs more than once, the Nkey attribute value will be smaller than the Ncard attribute value.

Type:

  Integer, read-only.

#### Applicability

##### FitsChan

All FitsChans have this attribute.
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