A brief history of metrology: past, present, and future

In this paper, we take the freedom to paraphrase Stephen Hawking's well-known formula and approach, for a reflection about metrology. In fact, metrology has a past, a present, and a future. The past is marked by a rich series of events, of which we shall highlight only those which resulted in major turns. The impact of the French Revolution is indisputably one of them. The present corresponds to a significant evolution, which is the entry of metrology into the world of quantum physics, with the relevant changes in the International System of units (SI). An apercu of the actual state of the art of metrological technology is given. The future is characterised by a persisting need for a still enhanced metrology, in terms of performance and domain covered. In this respect, soft metrology seems to constitute a promising field for research and development.