# 3.03 Summary

• The measurement value (or measurement) is the value given by a measuring instrument
• The true value is the actual value of the property being measured
• A measurement value does not specify a single exact value, it specifies a range of values within which the true value is believed to lie. This range of values is called the uncertainty interval or (simply the uncertainty).
• A measurement is expressed using the value at the midpoint of the uncertainty interval (nominal value) along with the difference either side to the limits of the uncertainty interval e.g. 10 +/- 0.5 cm
• Relative uncertainty is the size of the uncertainty compared to the size of the nominal value.
The smaller the relative uncertainty is the more precise the measurement is.
• Error is the difference between the measured value and the true value i.e. the difference between the true value and the furthest limit of the uncertainty interval.
• Relative error is the size of the error compared to the size of the nominal value.
The smaller the relative error is the more accurate the measurement is
• The accuracy and precision required for a measurement value depends on the particular application.