The jury is still out on a correction card, though...

I don't know the FAA rules, but in JAR (now EASA) country, the
regulation is:

JAR 22.1547 Magnetic direction indicator
Unless the deviation is less than 5° on all headings, the deviation
values for magnetic headings in not more than 30° increments must be
placarded near the magnetic direction indicator.


This of course only counts if the compass is part of the required equipment.