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Comment by gibibit | Hacker News Reader

"A single 1-kW jammer can take down GPS for a 300-nm radius.[...] A CRPA can shrink the effective radius of the 1-kW jammer to 3 nm. The jammer’s area of effectiveness is slashed from 280,000 m² to 28 m²."

An example of the kind of unit confusion that could crash a Mars orbiter?

I thought we were talking about nanometers and square meters here for a second. But this only makes sense if "m²" means square miles and "nm" means nautical miles. How about at least using "mi" for miles to reduce confusion?

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Well, nautical miles are the standard unit in the context of aviation, so I don't think it's all that bad. "mi" refers to a different unit.

True, "nm" initially seemed to be nautical miles, but then this square meters thing appeared. The point is that "m" should be meters, but "mi" would be a more customary abbreviation for miles in the U.S.

They shouldn't have switched from nautical miles to miles. The area should have been expressed in square nautical miles.

mile and nautical mile are not the same so it still doesn't make any sense

Agreed, though there's a space between the number & the unit which generally indicates non-SI units (SI should never have a space). The switch from nautical to statute miles is still really weird though.

Are you sure? NIST says there should be a space:

> There is a space between the numerical value and unit symbol, even when the value is used in an adjectival sense, except in the case of superscript units for plane angle.

https://physics.nist.gov/cuu/Units/checklist.html

> SI should never have a space

You are mistaken. SI units and their numbers always have a space. For reference [1], [2].

[1] https://www.npl.co.uk/si-units cf. Numerical Notation

[2] https://physics.nist.gov/cuu/Units/checklist.html cf. #15

EDIT: Scooped ;)

That's nonsense. There is a space between the number and the unit in SI.

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