3 ms·

It was only ever approximately accurate anyway, a NM is no longer an arc minute because that is inconsistent even along lines of latitude, so it had to be pinne

It was only ever approximately accurate anyway, a NM is no longer an arc minute because that is inconsistent even along lines of latitude, so it had to be pinned to 1.852km. Aviation, broadly speaking, inherited all of its navigation techniques from the maritime world. In particular, prior to radio methods and to some extent today aviation navigation is based primarily on dead reckoning periodically corrected by observations, which is a technique that was pioneered in marine navigation. Since early pilots learned to navigate from seafarers, their units and conventions became strongly embedded in the field. It is, after all, still not unusual to refer to an aircraft as a ship, especially informally.

deleted 5y ago
[deleted]
usrusr 5y ago
Ironically the metric system suffers the same theoretical "error" as the not-an-arc-minute-anymore NM because the meter was originally defined by taking the distance from pole to equator (to the best of their knowledge at the time) and then shifting the decimal point to get something human scale.
- mulmen 5y ago
  > to the best of their knowledge at the time I think it was actually extrapolated from a survey of the length of France. No idea how they did that extrapolation.
  - kergonath 5y ago
    Initially, yes. The story itself is quite fascinating, and the Wikipedia page on the metre is a good starting point. This was a hot topic during the 19th century as different improvements in the techniques and devices used to measure the Earth showed that the first measurements were imperfect, however good they had been at the time, and that the whole idea is not workable because the Earth is not a sphere. This lead to the formal definition of the metre as the length of a prototype in 1889.
    - usrusr 5y ago
      I imagine that the mental adjustment from sphere to almost but not quite a sphere must have been harder than a switch from flat earth to spherical. You just expect reality, if it matches a certain mathematical principle, to match perfectly.
- kergonath 5y ago
  This has not been the case since 1889, when the metre was formally defined as the length of a prototype metre bar. So the metric system has not suffered the same error for more than a century. Of course, the metric system has not been in use since 1960, but this is also true for the SI.

deleted 5y ago

[deleted]

usrusr 5y ago

Ironically the metric system suffers the same theoretical "error" as the not-an-arc-minute-anymore NM because the meter was originally defined by taking the distance from pole to equator (to the best of their knowledge at the time) and then shifting the decimal point to get something human scale.

mulmen 5y ago
> to the best of their knowledge at the time I think it was actually extrapolated from a survey of the length of France. No idea how they did that extrapolation.
- kergonath 5y ago
  Initially, yes. The story itself is quite fascinating, and the Wikipedia page on the metre is a good starting point. This was a hot topic during the 19th century as different improvements in the techniques and devices used to measure the Earth showed that the first measurements were imperfect, however good they had been at the time, and that the whole idea is not workable because the Earth is not a sphere. This lead to the formal definition of the metre as the length of a prototype in 1889.
  - usrusr 5y ago
    I imagine that the mental adjustment from sphere to almost but not quite a sphere must have been harder than a switch from flat earth to spherical. You just expect reality, if it matches a certain mathematical principle, to match perfectly.
kergonath 5y ago
This has not been the case since 1889, when the metre was formally defined as the length of a prototype metre bar. So the metric system has not suffered the same error for more than a century. Of course, the metric system has not been in use since 1960, but this is also true for the SI.