A portable roughness tester on a turned diameter says Ra 1.6 and the visual is a thread-like spiral. The print says Ra 1.6 and the buyer says the spiral fails regardless of the number. The cutoff length was the instrument default.
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A spiral you can see is a feed mark. Ra can still read 1.6 if the cutoff hides the waviness. Look at the trace, not only the Ra digit, and match the cutoff to the process. A turned surface needs the buyer to see the lay as well as the number.
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If the note is only Ra, you may be in spec and still lose the argument. Ask whether lay is controlled. If they say the spiral is the reject, the feed has to change, not the tester.
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Do not stone the spiral and retest a small patch. You are no longer measuring the process.
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