Talk:Nautical mile

message: The arcminute based on the Clarke 1866 ellipsoid is 1853.2480 metres, and was used to define the nautical mile by Britain and the US. But the 1929 Hydrographic Conference in 1929 went with 1852 metres. Was this because France and other countries were already using the arcminute at 45 degrees, i.e. 1852? Or did they have newer data? Perhaps the international ellipsoid that was developed by John Fillmore Hayford in 1910 and adopted by the International Union of Geodesy and Geophysics (IUGG) in 1924, which recommended it for international use? I haven't investigate what arcminute it gives. Perhaps 1852 was the generally accepted mean value by that time? --Cornellier (talk) 19:01, 30 August 2019 (UTC)
replies: text: I just investigated that by checking many issues of the Bureau des Longitudes' Annuaire on Gallica. From 1848 until 1909 1852 m was given as the length of a mille marin (nautical mile) without mentioning any ellipsoid (ellipsoids were described elsewhere without mentioning a nautical mile). From 1917 until  1952 it was stated that since 1906 the legal nautical mile for the French Navy has been 1852 m, calling it a "conventional value". Since 1933, this description has been amplified by stating "The nautical mile is in principle the length of the sexagesimal minute of a meridian at a latitude of 45°." However, it notes that that depends on the specific ellipsoid. Their last explanation is the real reason, "If we admit that the meter is exactly the ten-millionth part of the terrestrial quarter meridian, it would be equal to 1851.85 m." That has been true since about 1799. That value, rounded to 1852 m, was rubber-stamped by the 1929 International Hydrographic Conference. — Joe Kress (talk) 03:57, 31 August 2019 (UTC)

text: If you want to check other issues, a convenient clickable list of all Annuaires is at , accessed by clicking "see all issues" at lower left. After selecting an issue, click on the spyglass on the left edge, and enter the search term mille marin. The calculation is  = 1851.85 m, thus not dependent on any ellipsoid. — Joe Kress (talk) 06:13, 31 August 2019 (UTC)
replies: text: Thank you to Joe Kress and Cornellier for acting on my question above (#Gunter's definition).  Seeing your replies, I Googled for "nautical mile 6080 clarke" and found an article (The Nautical Mile PDF) by A. B. Moody in the International Hydrographic Review dated 1950.  It is a very clear and readable explanation of the history of the nautical mile, and it perhaps has other information which can be used to improve this article. JonH (talk) 14:49, 31 August 2019 (UTC)
thread_title:  Why 1852m in 1929? 

message: A nautical mile is 1852 metres. Since the SI definition of the metre has nine sig figs, one could in theory convert a nautical mile to 6,102.4 feet and 1.150779 miles. However, WP:OPCOORD states that the larger the object being mapped, the less precise the coordinates need to be, and recommends that a minute of arc be rounded to the nearest metre. Therefore the nautical mile should be expressed as "about 6102 feet" and "about 1.2 miles". --Cornellier (talk) 14:47, 1 September 2019 (UTC)
replies: text: since no opposition, updated article accordingly. --Cornellier (talk) 13:56, 29 September 2019 (UTC)
replies: text: WP:OPCOORD has no bearing on the question – it applies only to the size of objects on a map, not the units used to measure them. In this case the article has reference 16 by Astin and Karo giving the legal equivalent as 6076.11549 feet, so that should be in the article, citing reference 16. This is repeated by reference 2 alongside 1.1508 statute miles, so the latter should be in the article, citing reference 2. Reference 10 by Jerrard  defines the cable as 608 feet (1/10 nautical mile} at least one of which is wrong, so cable should not be in the article. — Joe Kress (talk) 01:37, 30 September 2019 (UTC)
replies: text:  I missed this proposal when first posted. Seeing as the nautical mile is exactly 1852 m, there's a clear justification IMO to quote more than 4 significant figures (not fewer) in any conversion. I think it would be helpful to mention an exact number of miles (or feet) somewhere in the article. For the info box I suggest using 5 sig figs: 1.1508 mi and 6076.1 ft. Dondervogel 2 (talk) 09:26, 30 September 2019 (UTC)
thread_title:  Significant figures in conversions