Error in Measurement –
The error in a measurement is equal to the difference between the true value and the measured value of the quantity.

Error = True value – Measured Value

Elimination of Error
The error may be positive or negative so random errors can be minimised by repeating measurements a large number of times. Thus the arithmetic mean of all measurement can be taken as the true value of the measured quantity.

a_mean = (a₁+a₂+…a_n)/n

Absolute Error –
The magnitude of the difference between the true value of the quantity measured and the individual measured value is called absolute error.