Relative error點解急急急急急急急急急急急急急?

relative error (相對誤差) :
-- it expresses the "relative size of the error" of the measurement in relation to the measurement itself.
-- relative error = ratio of the absolute error to the actual measurement.

公式：-
relative error = absolute error / actual measurement
relative error = | measured value - actual value | / actual measurement

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eg. A dog weighs 25 kg on a defective scale. Its actual weight is 26.5 kg.
In this measurement :

a.) absolute error = |25 - 26.5| = 1.5 kg
b.) relative error = 1.5 / 26.5 = 0.0566..... =0.057 (to 3 dec. places)

eg. In a game, Angus measures a string to be 98 cm long.
However, it is actually only 96.8 cm.
Then, relative error = | 98 - 96.8 | / 96.8 = .......

相對誤差