Two strategies for storing a date/time into a netCDF variable are:

1. as a string using a standard encoding and calendar (e.g. ISO 8601), OK for a single date/time
2. as a numeric value and a unit that includes the reference time, better for multiple times and makes it easier to compute differences between dates

Unidata's udunits package provides a convenient way to implement the second strategy.

• If your data uses real, physical time that is well represented using the Gregorian/Julian calendar, encode it as an interval from a reference time, and add a units attribute which uses a udunits-compatible time unit. Readers can use the udunits package to manipulate or format the date values.
• If your data uses a different calendar, use an existing convention such as the CF convention, or create a new convention which clearly documents what the calendar and encoding is. Make it compatible with existing date manipulation packages if possible (e.g. java.text.SimpleDate).
• Add multiple sets of time encodings if necessary to allow different readers to work as well as possible.

2008 Unidata NetCDF Workshop for Developers and Data Providers > Best Practices