If there was say a gyro spinning on a 3 point gimble moving through the atmosphere, every 15 - 20 minutes this gyro has to be realigned because it deviates off its original direction, say north.

I was told the gyro has to be realigned due of the friction of the bearings in the gimble. So I thought what if there were no bearings and it was spinning on magnets, air-bearings, frictionless...I was then told that it would still have to be realigned because of the coriolis effect.

Now I just learned today that the coriolis effect will not affect something smaller than say 300 feet or so, that is why small tornados do not spin all the same way, and this gyro is only 4 or 5 inches.

So can anybody tell me any other factor that could cause the gyro to deviate?