Magnetic reversal

writes:
Icebound wrote::

a.. Navigation without magnetic compass: gyro errors, finding & using the
sun's true bearing, and finding true north without celestial reference.

What about FMS and IRUs? Been around on the more sophisticated airliners
since the 767 came out in 1982 or so.

There are all sorts of things for the big boys, but what
do the small planes use?

What was used for small planes in the days before GPS?

I would think it would be a real challenge to fly the
Alaskan North Slope on a cloudy day (or night) without
at least GPS.