Let me rephrase less aggressively: If you pick a "zero" tolerance, that's saying your measurement can actually be zero and there's no need to improve from that

Let me rephrase less aggressively: If you pick a "zero" tolerance, that's saying your measurement can actually be zero and there's no need to improve from that point. If you pick a measurement that can only asymptotically approach zero, then you are recognizing that improvement is always possible.