I've been reading up on gravity probe B and the results, but I have a question about precession in general - I've heard it said that since the gyroscopes are in free fall there is no classical precession to be expected. So then, what explanation was there for earth's precession before general relativity? We knew about earth's precession long before einstein was around. Surely there was a classical model for earth's precession, right? That seems like a big hole in newton's theory if we knew about the earth's precession but couldn't explain it.