The ‘nec plus ultra’ of precision measurement: Geodesy and the forgotten purpose of the Metre Convention

Geodesy—the determination of the size and shape of the earth—has often been the science operating at the frontier of precision in the measurement of length. Its contribution to the technologies and standards of length measurement has, however, been underestimated in the literature. That, instead, places emphasis on the on the creation and international acceptance of the metric system as a whole. By new research into the standards-in-use of the community of geodesists, I rediscover the original purpose of the Metre Convention of 1875, and show for the first time the significant influence of geodesy on the standardisation of length measurement thereafter. I emphasise the role of the coherence of the web of measurement in the context of change and improvement in standards.

► I examine the contribution of geodesy to techniques and standards of precision length measurement.
► That allows rediscovery of the original, geodetic, purpose of the Metre Convention of 1875.
► The International Metre created by that convention is shown to be the first global étalon of length.
► I emphasise the role of the coherence of the web of measurement in the context of change in standards.