©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 26
The expanded uncertainty
• As mentioned, calculations for u
c
pertain to ± one standard
deviation of measurement uncertainties (covering 68% of the
population of measurements)
• Usually it is desired to express uncertainty for a larger population or
condition, say 95% or 99%.
• Expanding the calculated uncertainty through scaling estimates an
uncertainty that covers this larger population - U
m
.
• A coverage factor, k, (often equal to 2), would indicate a 95%
confidence.
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