ATP is measured in relative light units (RLU), which are obtained from the number of photons produced from ATP reacting with Luciferin. The more ATP on the swab, the more photons were created, so the lower the RLU the better. The more ATP present on the swab, the more photons are created. If the RLUs exceed the specifications, then the item must be cleaned again and then swabbed again until the RLUs are within an acceptable range.
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