A systematic error is caused by a defect in the analytical method or by an improperly functioning instrument or analyst.
A procedure that suffers from a systematic error is always going to give a mean value that is different from the true value. The term 'bias' is sometimes used when defining and describing a systematic error. The measured value is described as being biased high or low when a systematic error is present and the calculated uncertainty of the measured value is sufficiently small to see a definite difference when a comparison of the measured value to the conventional true value is made.
Some analysts prefer the term 'determinate' instead of systematic because it is more descriptive in stating that this type of error can be determined.
A systematic error can be estimated, but it cannot be known with certainty because the true value cannot be known. Systematic errors can therefore be avoided, i.e., they are
Sources of systematic errors include spectral interferences, chemical standards, volumetric ware, and analytical balances where an improper
calibration or use will result in a systematic error, i.e., a dirty glass pipette will always deliver less than the intended volume of liquid and a chemical standard that
has an assigned value that is different from the true value will always bias the measurements either high or low and so on. The possibilities seem to be endless.