Measurement error refers to the difference between the actual value of a quantity and the value obtained through measurement. This error can arise from various sources, including instrument inaccuracies, environmental conditions, or human mistakes. For example, a thermometer may give a slightly different reading due to calibration issues or temperature fluctuations. There are two main types of measurement error: systematic and random. Systematic errors occur consistently in the same direction, often due to faulty equipment or biases in measurement techniques. In contrast, random errors vary unpredictably and can be caused by factors like observer variability or changes in the environment during measurement.