Amazing how this becomes complicated.
Go to a compass manufacturer website, download a manual and go to deviation or compensation.
The rest is SO simple if you pick a good area and conditions to do it in.
To compensate your compass, follow the below....then just modify it to do your deviation table by doing it in 10 to 20 degree or so pie cuts,
Straight frim Ritchie compass website....
1. While at sea, with the compass in its intended position, but not
fully secured, obtain the Loran/GPS bearing to a visual buoy or
landmark that is within 10 degrees of the North/South line.
2. Position your
boat along that line and steer it directly at the
mark. Turn the port/starboard compensator until the compass
heading matches the Loran/GPS bearing.
3. Check the Southerly course by
steering away from the mark,
to a bearing 180 degrees from step 2. If an alignment error
is detected, rotate the compass itself to correct for half of this
error. Then repeat steps 1 and 2 and recheck.
4. Repeat steps 1-3 for the East/West course, using the fore/aft
compensator. Any alignment error should have been eliminated
during the initial part of the procedure.
5. When finished, secure the compass in its final position.
*When using this method, always use the bearing
"To or From" on the Loran/GPS. Do not use the
heading information because it is inaccurate in
real time.
If you have trouble achieving compensation,
contact a reputable compass adjuster. Once
you've achieved proper compensation, this
would be the ideal time to check for deviation
and complete your final deviation table.