Scientists always try their best to record measurements with the utmost accuracy and precision. However, sometimes errors do occur. These errors can be random or systematic. Random errors are observed due to the inconsistency or fluctuation in the measurement process, or variations in the quantity itself that is being measured. Such errors fluctuate from being greater than or less than the true value in repeated measurements. Consider a scientist measuring the length of an earthworm using a ruler. Random error in this measuring process could be the result of the inconsistent method in which the scientist reads the scales, or if the earthworm is moving. Random error cannot be avoided; however, it can be averaged out with repeated trials.

Systematic errors arise from a persistent issue and result in a consistent discrepancy in measurement. These errors tend to be consistently either greater than or less than the true value. These are predictable and are mostly instrumental in nature. For instance, an improperly calibrated weighing balance may consistently weigh objects heavier than their true value. Unlike random error, systemic errors cannot be averaged out with repeated measurements.

This text is adapted from Openstax, Chemistry 2e, Section 1.5: Measurement Uncertainty, Accuracy, and Precision.