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Hi Sue, There are still instances in netCDF-4 where define mode is important. for example setting compression characteristics of a variable. The documentation you cite doesn't make this clear, but later in the User's Guide, this appears: <http://www.unidata.ucar.edu/software/netcdf/netcdf-4/newdocs/netcdf-c.html#Adding> For netCDF-4/HDF5 format files, define mode is still important, but the user does not have to called nc_enddef - it is called automatically when needed. It may also be called by the user. In netCDF-4/HDF5 files, there are some settings which can only be modified during the very first define mode of the file. For example the compression level of a variable may be set only after the nc_def_var call and before the next nc_enddef call, whether it is called by the user explicitly, or when the user tries to read of write some data. I hope that answers your question. We probably need to make another pass on the documentation to make sure it still presents a simple model to users of netCDF-3 or the netCDF-4 classic model, but lets adventuresome netCDF-4 users know about the extra power (and complexity) of the new features. One way to do this is to occasionally oversimplify the situation by presenting the classic model of how things work, and later fill in the details ... --Russ Russ Rew UCAR Unidata Program address@hidden http://www.unidata.ucar.edu Ticket Details =================== Ticket ID: OBB-868168 Department: Support netCDF Priority: Normal Status: Closed