[throwawaylinux]

I'm not a sea dog (or air dog), but even absent electronic calculation and navigation devices of the last half century or so, is there any real advantage to using nm vs any other unit? Other than for the presumably niche case of traveling exactly directly along the equator, that is.

nm are great because charts and speeds are in units of nm and kt of course, but what does "real meaning" give you exactly?

[kuhewa]

Am sea dog, I think it's just a little bit of smugness. Because it doesn't generally help (besides quickly estimating latitudinal distance or near-equatorial distance), unless you are actually doing dead reckoning with a chart or similar, which is rare today.

The equivalency with knots is great and all but it too is just a convention

[ryandrake]

To be precise, a nautical mile is always a minute of latitude, everywhere on earth. It is only a minute of longitude at the equator.

[throwawaylinux]

Ah, good point. In that case expand the niche cases to traveling due north or south.

[jabl]

In practice, when navigating by pen and paper, what you do is you measure a distance on the chart with a divider, then you put the divider (with the previously measured distance set) to the north-south scale on the side of the chart to read out the distance in nautical miles.

Now, of course, in principle charts could have a separate scale for distances in km, and we could use km for navigation just fine. But, well, I've never seen a nautical chart with such a scale.

[wkat4242]

And, at sea level. At altitude this no longer applies either because the circumference at altitude is greater.

[closewith]

Well, it still applies in aviation, as distance and ground speed used in navigation are measured at sea level irrespective of altitude.

[pbmonster]

...by around 0.1%. Which is why nobody is bothering with it, considering how susceptible to wind speed distances and velocities are up there.

[ianburrell]

I think the only advantage is when using old navigation devices. You measure altitude of sun at noon and that is your latitude, time of noon is your longitude. It also only works when going east-west, it falls apart any other angle.

These days, everybody has plotter or phone to measure position and speed and calculate distances.

[yread]

It fits with the other unit: 1 knot is 1 minute of latitude per hour