Systematic error
From Glossary of Meteorology
systematic error
That part of the inaccuracy of a measuring instrument, or statistical estimate of a parameter, that is due to a single cause or small number of causes having the same sign, and hence, in principle, is correctable; a bias or constant offset from the true value.
In the absence of random errors, the true value is equal to the instrumental reading or statistical mean estimate minus the systematic error.
