Automatic HISTORY Creation

The NDF data format offers a means by which processing commands and user comments may be recorded, so that at some future time you can determine how a given NDF was created. History recording is optional.³ However, now massive storage is cheap we recommend that you routinely use NDF history recording.

History recording may be enabled on an NDF-by-NDF basis using the KAPPA command HISSET as described in the NDF History section of SUN/95. In the case of CONVERT this has a disadvantage--the CONVERT conversion command will be absent from the NDFs created by the $x$2NDF commands. If you wish that all new NDFs created by CONVERT have history recording enabled at their creation, you should set the environment variable NDF_AUTO_HISTORY to a non-zero integer value. In fact, we recommend that you set this in your login script so any NDF created from scratch will have this property.