Why do some people write: 1 mg kg (-1) instead of just 1 mg/kg?

[DeeJay]

The (-1) of course being a superscript. I mean, I know what it means literally, but why not just use the slash? Is it not correct enough?

[ArcticFox]

1. Why don't people write mi/hr instead of mph?

[DeeJay]

3. I don't know.

Maybe because mph has to be included on car invoices and stickers, and maybe they are trying to conserve space by using 2 fewer digits? :shrug:

[Cronus Protagonist]

2. Because the slash character is an escape in PERL?

Causes scripts to be harder to handle... :-\

[DeeJay]

4. That is a good possibility.

Old habits die hard maybe?

[Igel]

6. Predates PERL.

Predates SNOWBOL.

Hell, it predates transistors.

[Igel]

5. It keeps it on one line.

It's not so bad with just mg/kg, but J/g K might be confused. Or should that be J/g/K?

J g^-1 K^-1 is utterly unambiguous (when properly typeset) even when on one line. Once you have the "style" guide dictating that J/g K has superscripts, then mg/kg falls under the rule as well--otherwise you'd have to ask why some have the superscript and others don't.

I stopped noticing the difference when I was 17.

[TheMadMonk]

7. Standardisation of notation.

m/s/s is also "legal" but it's just not a form of notation used. ms^-2 is how it's done. G (the gravitational constant) is measured in units of m^3 kg^-1 s^-2. Try expressing that in slash notation.

x per y tends to be a special case in spoken language and informal writing, but standard notation is still much preferred in publication.