Final answer:
A magnetic compass should be locked into a constant heading when not in use for a prolonged period of time to prevent inaccurate readings.
Step-by-step explanation:
A magnetic compass should be locked into a constant heading when not in use for a prolonged period of time.
Locking the compass into a constant heading means ensuring that the compass needle is aligned with the Earth's magnetic field lines. This prevents the needle from becoming magnetized in a different direction and causing inaccurate readings.
For example, if the compass is left in a random heading for a long time, the needle may become magnetized by nearby magnetic objects and no longer accurately point to the north.