what's the meaning of this?
A margin for error so substantial and so sacrosanct as to make the error itself unthinkable. An air traffic controller's dominion may be up in the air, but there is precious little else in his world that is.That is the point.

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The first sentence is not complete one as it has no main verb - I suspect there must be more to this sentence.  Can you post the full sentence, or even better, the whole paragraph?

This is advanced English.  If you are an advanced learner, you should be able to make some sense of it and tell us what you think it might mean.  If you do this, then we can help you to improve your understanding.