On being sufficiently exact: assessing navigational instruments in the eighteenth century.

This paper explores discussions centred on the activities of the British Board of Longitude to consider the ways in which some men of science, instrument makers and others thought about questions of precision and accuracy, both in principle and in terms of what was possible in practice when making observations at sea. It considers firstly the terminology used in some eighteenth- and early nineteenth-century texts, highlighting the concept of exactness, which was more commonly used to describe one of the desirable qualities of instruments and methods. It then looks at some of the discussions and debates in which the Board of Longitude was involved from the 1760s to think about different actors' expectations of what levels of exactness might be either desirable or possible for day-to-day navigation. The focus is on the ability to make accurate shipboard observations and on the question of what degree of exactness might have been accepted as good enough for routine navigational purposes when at sea.