[labcomputer]

> they still have massive drift after several hours. If you don't have GPS to relocalize precisely at least every day

I think you may be confusing two concepts: Measurement of true north and latitude via gyro (what the GP is talking about) and inertial navigation systems (which, yes, do drift).

You can measure those two things with just a single-axis gyro and no external references using a technique called "gyro-compassing". In fact, most internal navigation systems use gyro-compassing to directly measure true north and latitude to align the system on initial startup.