I am not sure what you are trying to do here. Attribute names beginning with an underscore ('_') are reserved for the use of netcdf and I do not think the attribute _Netcdf4Dimid is used by netcdf. Can you give some details of what you are trying to accomplish with this attribute? =Dennis Heimbigner Unidata =Dennis Heimbigner Unidata Ticket Details =================== Ticket ID: QMB-725319 Department: Support netCDF Priority: Normal Status: Closed