While the quest for increased accuracy may be driven by the needs of applications, the effort to achieve accuracy of measurement itself stimulates other developments, in terms of measuring instruments and systems, and in terms of the understanding of the very nature of measurement. ‘Measurement and understanding’ explains that there are two fundamental aspects to measurement accuracy: precision (how much repeated measurements fluctuate about a central value) and bias (any systematic departure from the underlying true value, affecting all repeated measurements). It also discusses measurement and statistics and how representational measurement leads to some very deep and powerful tools for constructing models and theories about how the world works.