Answer to Question #598 in Statistics and Probability for Tamy
Distinguish between a systematic and a random error in the measurement of a physical quantity.
Random measurement errors of the same physical quantity if small, should over time cancel, while systemic measurement errors will not.
Reading an instrument may produce random errors. If the same person reads it, there is a chance of systemic errors, so having separate individuals make independent readings is one way of reducing systemic error.
Errors in calibration of equipment produces systemic errors. Sometime minor flucuations in environment causes highly sensitive equipment to generate random errors. However, using an instrument in an environment that is outside its working range can cause systemic errors.