Module description: Measurement data acquisition is done through the use of various instruments with particular properties. The instruments are error prone and the data they provide has a significance and degree of precision that depends on the instrument. Therefore, it is an important step in the research process to know whithin what range acquired data is usable. This is done through calibration of the measurement instrument, a process that also includes tests for reproducibility. In most cases acquired measurement data should be provided together with some kind of error model.