GG's:

For decades, the U.S. Navy Hydrographic Office issued a hardbound handbook for
magnetic compasses.  A quick search revealed that it has been superseded by an
on-line pdf file from a different agency:

download ( https://msi.nga.mil/api/publications/download?key=16920950/SFH00000/H
oMCA.pdf&type=view )
PDF Document · 2 MB ( https://msi.nga.mil/api/publications/download?key=16920950
/SFH00000/HoMCA.pdf&type=view )

( https://msi.nga.mil/api/publications/download?key=16920950/SFH00000/HoMCA.pdf&
type=view )

John Ruth
Metuchen NJ