Editing Spirit level (section)

==History==
{{More citations needed section|date=December 2024}}
The history of the spirit level was discussed in brief in an 1887 article appearing in ''[[Scientific American]]''.<ref>{{Cite book|url=https://books.google.com/books?id=moM9AQAAIAAJ|title=Scientific American|date=1887-08-27|publisher=Munn & Company|pages=136|language=en}}</ref> [[Melchisédech Thévenot]], a French scientist, invented the instrument some time before February 2, 1661. This date can be established from Thevenot's correspondence with scientist [[Christiaan Huygens]]. Within a year of this date the inventor circulated details of his invention to others, including [[Robert Hooke]] in [[London]] and [[Vincenzo Viviani]] in [[Florence]]. It is occasionally argued that these "bubble levels" did not come into widespread use until the beginning of the {{nowrap|18th century{{hsp}}{{mdash}}{{hsp}}}}the earliest surviving examples being from that {{nowrap|time{{hsp}}{{mdash}}{{hsp}}}}but [[Adrien Auzout]] had recommended that the [[Académie Royale des Sciences]] take "levels of the Thevenot type" on its expedition to [[Madagascar]] in 1666. It is very likely that these levels were in use in France and elsewhere long before the turn of the century.

The Fell All-Way precision level, one of the first successful American made bull's eye levels for machine tool use, was invented by [https://patents.google.com/patent/US2211201A/en William B. Fell of Rockford, Illinois in 1939].<ref>{{cite web|url=https://patents.google.com/patent/US2316777A/en|title=Machinist's precision level (US2316777A)|author=William B Fell|date=1940-08-01|publisher=[[Google Patents]]|access-date=2 August 2018}}</ref> The device was unique in that it could be placed on a machine bed and show tilt on the x-y axes simultaneously, eliminating the need to rotate the level 90 degrees. The level was so accurate it was restricted from export during [[World War II]]. The device set a new standard of .0005 inches per foot resolution (five ten thousands per foot or five arc seconds tilt). Production of the level stopped around 1970, and was restarted in the 1980s by Thomas Butler Technology, also of Rockford, Illinois, but finally ended in the mid-1990s. However, there are still hundreds of the devices in existence.