| Name | Description |
| The following keywords are REQUIRED for Calnic Cto run. | |
| EXTEND | States file may contain extensions |
| NEXTEND | Number of extensions should be 5 for NICMOS data files |
| XTENSION | For the 5 extensions this should be 'IMAGE' |
| EXTNAME | Actual data stored in current extension (SCI/ERR/etc) |
| EXTVER | Extension version (not used currently but should be 1) |
| ROOTNAME | Rootname of observation set. Used for output file names |
| FILTER | Name of the filter/grism used in observation |
| The following keywords are not required but some | |
| functionality depends on them. | |
| ADCGAIN | Analog/digital conversion gain |
| BACKEST1 | Background estimate 1 |
| BACKEST2 | Background estimate 2 |
| BACKEST3 | Background estimate 3 |
| CRPIX1 | x-coordinate of reference pixel |
| CRPIX2 | y-coordinate of reference pixel |
| CRVAL1 | First axis value at reference pixel |
| CRVAL2 | Second axis value at reference pixel |
| CTYPE1 | The coordinate type for the first axis |
| CTYPE2 | The coordinate type for the second axis |
| CD1_1 | Partial of first axis coordinate w.r.t. x |
| CD1_2 | Partial of first axis coordinate w.r.t. y |
| CD2_1 | Partial of second axis coordinate w.r.t. x |
| CD2_2 | Partial of second axis coordinate w.r.t. y |
| EXPTIME | Commanded exposure duration |
| PHOTFNU | Inverse sensitivity (JY*sec/DN) |