[bufrtables] Diff tables

Is there any existing documentation for the format of a .diff table (like 
ncep.B4L-007-013-D.diff) that is referenced in the netcdf-java 
bufr.src.main.resources.resources.bufrTables.local.ncep directory in the 
thredds bundle? Do I need to just work through the source code or is there an 
explanation of the format somewhere? I am working through decoding some ARINC 
messages that do not decode with the current table set and need to modify some 
tables.

Randy Pierce