Experimental error is the difference between a measured value of a quantity and its true value. It is an inherent part of the results of measurements and of the measurement process, and it can be caused by a variety of factors, including:
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Systematic error: This type of error always occurs with the same value when the instrument is used in the same way and in the same case. It may often be reduced with standardized procedures.
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Random error: This type of error may vary from observation to observation. It is caused by unpredictable fluctuations in the readings of a measurement apparatus or in the experimenters interpretation of the instrumental reading. Random errors can be estimated by comparing multiple measurements and reduced by averaging multiple measurements.
Experimental error should not be confused with measurement uncertainty, which is a measure of the range of values within which the true value of a quantity is expected to lie with a certain level of confidence. It is important to estimate the experimental error likely to be present in order to use data wisely, whether the data being considered were measured personally or merely read from manufacturers data sheets for a material or component. Reported experimental results should always include a realistic estimate of their error, either explicitly, as plus/minus an error value, or implicitly, using the appropriate number of significant figures.
