Let the true value of a quantity be and the measured or inferred value . Then the relative error is defined by
where
is the absolute error. The relative error of the
quotient or product of a
number of quantities is less than or equal to the sum of
their relative errors. The percentage error is
100% times the relative error.
and the measured or inferred value 
. Then the relative error is defined by
is the absolute error. The relative error of the
quotient or product of a
number of quantities is less than or equal to the sum of
their relative errors. The percentage error is
100% times the relative error.
