One of the ten best scientific instrument makers in Britain during the second half of the eighteenth century.

Ramsden's skill and talent for making instruments was quickly recognised and he became an established manufacturer in London during the 1770s and 1780s.

Ramsden's most important invention was the 'dividing engine', a machine for accurately obtaining division of angular and linear scales on instruments. His second dividing engine in 1775 greatly speeded up the production of instruments with more consistent accuracy.

Such was Ramsden's reputation that between 1784 and 1791 he was commissioned to construct 3-foot (91 cm) theodolites of the highest quality with unprecedented accuracy for detailed map-making.