ACS Analytical Chemistry Practice Exam

Systematic error is a bias that shifts all measurements by roughly the same amount in a given direction due to a flaw in the instrument, procedure, or calibration. The idea is that the error consistently biases results, so measurements cluster high or low relative to the true value. For example, a balance that isn’t zeroed or a spectrometer with a constant baseline offset will produce readings that are systematically too high or too low. This persistent directional shift distinguishes systematic error from random error, which causes measurements to scatter unpredictably around the true value. When measurements vary randomly—sometimes high, sometimes low—they reflect random error, not a fixed bias. The statement that measurements are usually high or always low captures that consistent bias. It isn’t accurate to say systematic error cannot be corrected; once the bias source is identified, calibration, method adjustments, or data correction can often remove or reduce it.