I want to add the diameter symbol, as described there Diameter on Wikipedia in my equation:
begin{equation}
\diameter~Aufwand~in~\% = \frac{\diameter~Aufwand~in~ZE~f"ur~die~Testt"atigkeit}{\diameter~Aufwand~in~ZE~f"ur~die~Entwicklung}
\label{equ:Durchschnittlicher-Aufwand}
\end{equation} \par
Therefore i used the packages as desribed there usepackage
\usepackage{amsmath,amsthm,amssymb}
3 times I got an error like this:
! undefined control sequence
l.XX \diameter
Can you give me some hints, what I should change or what can be the problem? I have no idea...

wasysym. – Tanvir Jun 27 '20 at 13:09