The -grid_changes option is a safety option.
Normally we don't expect the grid to change within a file. Many
programs would fail if the grid did change. This option prints
to stderr, the number of times the grid changed within the file.
$ wgrib2 fcst.grb2 -bin fcst.bin -grid_changes -count
-sh-3.00$ wgrib2 fcst.grb2 -bin fcst.bin -grid_changes
2:422561:d=2007032600:HGT:1000 mb:3 hour fcst:
Good: only one grid
number of records: 2
In the above example, we converted the file to binary. It consisted
of a single grid and two records.