A multiplicative error is proportional to the true value of the quantity being measured. An example of a multiplicative error is when electronic scales provide readings 1% higher than the true weight - i.e. 1.01 kg for 1.0 kg standard weight, 2.02 kg for a 2.0 kg standard weight, etc.
is the result of a measurement of some quantity, say, weight;
is the true value of the quantity;
is relative value of the multiplicative error, often expressed in percent, e.g instead of is is normally said that the error is 1%.
A related concept is additive error ,
See also the short courses