Jim Macklin wrote:
I'm speaking of the question by the OP, which seemed to be
asking if all you had was the compass or the TC [needle],
which would be primary.

In straigtht and level flight under partial panel the compass would
have to be primary because the TC cannot tell you if you are still on
the correct heading. Corrections would be made with the TC though. Just
like full panel when your DG is primary in straight flight. It is very
possible to roll out to a heading within 2 degrees in any direction
using "compass turns" technique.

-Robert, CFII