[Tex/LaTex] Problem with units in math mode

Question

I'm having problems with the following equation:

\[\frac{dT(t)}{dt} =-1^{\circ}F \text{per hour}\]

it displays:

How do I make "per hour" in normal text form rather than italicized?

Answer 1

Use the siunitx package to write correctly units. It works in both text and math modes.

Default is to use negative exponents instead of a fraction. You can force the use of a symbol by using the \SI command option per-mode=symbol. You can also set the behavior for all units with \sisetup.

Code

\documentclass{article}

\usepackage{mathtools}

\usepackage{siunitx}
\DeclareSIUnit{\fahrenheit}{\SIUnitSymbolDegree F}
%\sisetup{per-mode=symbol}


\begin{document}

    \[\frac{dT(t)}{dt} = \SI{-1}{\fahrenheit\per\hour}\]
    \[\frac{dT(t)}{dt} = \SI[per-mode=symbol]{-1}{\fahrenheit\per\hour}\]

\end{document}

Result

Out-of-the-scope advice

In well formatted maths, the d of derivative should be upright, not slanted. To do so:

\[\frac{\mathrm{d}T(t)}{\mathrm{d}t} = \SI[per-mode=symbol]{-1}{\fahrenheit\per\hour}\]

Enjoy!