The General Conference on Weights and Measures (CGPM) defines the length of a metre

The General Conference on Weights and Measures (often abbreviated as CGPM, from its French name Conférence Générale des Poids et Mesures) is an international organization that plays a crucial role in maintaining and developing the International System of Units (SI). It is responsible for decisions regarding the international standards of measurement, ensuring that measurements made in different parts of the world are consistent and reliable.