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Comment by tombh | Hacker News Reader

'nm' is 'nautical mile', for anyone wondering

Clearly a mistake. Abbreviations for nautical mile are M NM or nmi. I guess the author has not heard about nanometer

I guess you could take the context of the article. There would be no way to measure in nanometers in that situation. So if someone does not know that nautical miles was implied, it should be easy to infer that nm was not nanometer.

I did infer that, but was extremely confused because I didn't know what else it could be.

The source isn't really intended for general consumption. It's a briefing intended for pilots and others in the industry. The goal of these kind of documents is to help pilots and air traffic controllers to learn from their mistakes.

Sure, but that didn't stop me from thinking "nanometer" whenever I saw it. Initially, I was wondering what font screwup could turn "km" into "nm".

Same! I was wondering A) how in the world they managed to get that closr and B) how they managed to measure it.

In an aviation context, `nm` is almost universally used for (and understood to mean) nautical mile.

NM or nmi, but not nm.

Confusion in units is never a good thing.

The FAA uses "NM" (capitalized) in federal regulations.

I don't think I've ever seen someone use M, NM, or nmi for nautical mile. I've only ever seen nm. I used nautical miles a lot in a previous career, in the context of aircraft mission planning.

Telling people in the industry to use nmi or NM seems a lot like telling computer people to use MiB or GiB instead of MB or GB, or to pronounce gif "jiff". They're just not going to change.

It is going to change. I use MiB and GiB. I also use the ISO standard for dates, etc. Precisely because they are now standard.

Saying it is not going to change is what makes things harder.

The aviation industry: not exactly sticklers for metric usage.

The Apollo flights used NM on their screens for nautical mile.

[pic (right-most screen)] https://cdn.arstechnica.net/wp-content/uploads/2012/10/liebe... [article] https://arstechnica.com/science/2019/12/apollo-flight-contro...

Also "KFPS", presumably for "thousands of feet per second"

Nautical miles are a fun unit. They are one minute of arc of the earth's surface (idealized), so it makes sense why they took hold in the two forms of travel that regularly travel great circle routes.

There is a similar relationship between gradians (metric angles) and kilometres https://en.wikipedia.org/wiki/Gradian

One minute of latitude for those wondering how this works.

Thank you! I was wondering how these work around the poles!

1nm is about 1/60th of a degree of any great circle on the earths surface

(Earth isn’t a sphere so it’s not exact, but it’s pretty close)

Yeah I did a double take. Close but surely not that close.

missed by a whisker -> 90,000 nanometers apart

Thanks. 2 nanometers of distance would indeed be a bit low.

It's only a problem if the planes are both fermions.

Not nano meter :)

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