Real measurements are never made under perfect conditions. Errors and uncertainties can come from:

• The measuring instrument – bias, drift, noise etc
• The condition being measured – which may not be stable
• The measurement process- may be problematic
• Imported uncertainties e.g. calibration uncertainty
• Operator skill
• Sampling issues
• The environment – temperature, air pressure

Uncertainties can come from each of these sources contributing to the overall uncertainty in the measurement.

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Good practice online modules

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• Measurement uncertainty
• Introducing uncertainty
• Basics of uncertainty analysis