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 (SUN/95) 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 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.
3This was because at the time it was created history records could potentially be quite bulky for spectra.