What is the purpose of duplicate field measurements and how are they used?

• A. A backup measurement in case the first result is inconclusive.
• B. Measuring two different surfaces to compare results.
• C. A protocol to discard outliers after a single measurement.
• D. A second measurement on the same surface to assess measurement repeatability and method precision.

Answer: (D)

Taking a second reading on the same surface shows how repeatable the measurement is and how precise the method is. In the field, small differences can creep in from the instrument, the way you hold or position it, or environmental factors. By duplicating the measurement, you can see whether the results come out nearly the same each time or if they vary a lot. If the two readings are close, it demonstrates good repeatability and gives you more confidence in the data and the procedure. If they differ significantly, it flags potential issues with the instrument, technique, or conditions that should be investigated before you rely on the measurement for lead clearance decisions. This approach specifically monitors consistency, rather than simply backing up a single result, comparing surfaces, or discarding outliers after just one measurement.