what is the symbol for : absolute error
mean absolute error

relative error 

Absolute error : Absolute error in the measurement of a physical quantity is the magnitude of the difference between the true value and the individual measured value of the quantity.If a quantity is measured n times.Let the measured values be a₁, a₂,a₃......a_n.If a_m is the arithmetic mean of these value then the absolute errors in the individual measured values of the quantity can be written as :

The absolute errors may be positive in certain cases and negative in certain other cases.

 

Mean absolute error: It is the arithmetic mean of the magnitudes of absolute errors in all the measurements of the quantity(we ignore the sign of absolute errors) . It is represented by Δa_mean.

 

Relative error: The relative error of measurement is the ratio of mean absolute error to the mean value of the quantity measured.It is represented by δ_a.