A systematic error is the mean of a large number of measurements of the same value minus the (probable) true value of the measured parameter. (VIM, 3.14) Systematic error causes the average of the readings to be offset from the true value. Systematic error is a measure of magnitude and may be corrected. Systematic error is also called bias when it applies to a measuring instrument. Systematic error may be evaluated by Type A or Type B methods, according to the type of data available. Note: Contrary to popular belief, the GUM specifically does not replace systematic error with either Type A or Type B methods of evaluation. (3.2.3, note) See also: bias, error, correction (of error) Compare with: random error