 Nonetheless, for many years even towards the end of the 18th century, chronometers were expensive rarities, as their adoption and use proceeded slowly due to the high expense of precision manufacturing.The expiry of Arnold's patents at the end of the 1790s enabled many other watchmakers including Thomas Earnshaw to produce chronometers in greater quantities at less cost even than those of Arnold.By the early 19th century, navigation at sea without one was considered unwise to unthinkable.