In a measurement, the absolute value of the difference ε between the approximate value α and the theoretical value x.
In theory, an absolute error is the difference between a theoretical value and an experimental value. It should be noted that a real value can never be obtained through measurement; a measurement is an approximation whose limits are determined by the precision of the measuring instruments and by the care taken by the person carrying out the measurement. In practice, an absolute error is obtained by calculating the mean variation from a set of measurements of the same quantity.
The difference between the approximate value α and the exact value x is denoted by ε, the Greek letter epsilon.
ε = |α − x|.
A theoretical distance of 28 cm was measured at 27.84 cm. The absolute error is equal to 0.16.