The En value may differ because the values used in the calculation by the participant and by NAPT are not always identical. The values used on both preliminary and final reports are calculated in accordance with ISO 13528 to ensure accuracy and consistency.
For participants, the reported resolution is influenced by the resolution of the artifact being measured or a reference standard, as well as any significant digit considerations. It’s also important to note that preliminary reports do not include an En value; therefore, any concerns about En calculations based on a preliminary report are irrelevant. Remember, the purpose of the preliminary report is solely to confirm that the values submitted by a participant have been accurately reported to NAPT, allowing NAPT to perform an initial analysis of the data submittal. This step also enables NAPT to identify any potential gross errors and take appropriate action if needed.
The values in a preliminary report are, by nature, preliminary. The language within the report clarifies in detail that these values are subject to change. When NAPT issues the final report, the values may be truncated or rounded based on the resolution of the artifact reference standard and any relevant significant digit factors.
For a participant to match NAPT’s En calculations precisely, they must use the exact values that NAPT applies in their analysis. For example, if an artifact’s value is recorded to three decimal places in our final report, but a participant records to five decimal places, the report will reflect only three decimal places, though NAPT retains the full precision internally for calculation purposes. The same principle applies to the assignment of the established reference uncertainty, which is typically reported by NAPT at one resolution level higher than the measurement made by the participant, following standard reporting practice.
To ensure that your En calculations align exactly with those from NAPT, you must use the identical values and rounding conventions NAPT employs in its calculations. If needed, please feel free to contact NAPT to obtain the exact numbers used in any specific calculation.