FWIW, state-of-the-art INS is not publicly available technology. No one knows what the real limits are, only that it is much less than what is available publicl

FWIW, state-of-the-art INS is not publicly available technology. No one knows what the real limits are, only that it is much less than what is available publicly. Cheap systems like guided bombs use conventional laser gyros but they don’t need to maintain their precision very long and they only accept GPS corrections within their drift error (a dozen meters?). When real precision is required, they tend to use laser guidance anyway.