\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows}
\usetikzlibrary{positioning}
\usetikzlibrary{calc}
\begin{document}
\tikz \fill[green] rectangle (0.5,0.5); Something
about something.

\begin{tikzpicture}
  \draw [solid] let \p{I} = (0,0) in (1,1) -|
    (\x{I}-1cm,-1cm) node [yshift=-.25cm] {(i)};
  % Just some comment
\end{tikzpicture}

\begin{tikzpicture}
  % (i) center contact head
  \draw [solid] let \p{I} = (centerContactHead) in (centerContactHead) -|
    (\x{I}-.75cm,-2.5)
    node [yshift=-.25cm] {(i)};

  % (ii) outer conductor of the contact head
  \coordinate (outerContactHead) at (.8,-1.7);
  \draw [solid] let \p{O} = (outerContactHead)
    in (outerContactHead) -- (\x{O},-2.5)
    node [yshift=-.25cm] {(ii)};

  \begin{axis}
    \addplot
      table[row sep=crcr]{%
        0       0\\
        1       1\\
        2       2\\
      };
  \end{axis}
\end{tikzpicture}

\begin{center}
  \begin{circuitikz}[american]
    \draw (0,0) node[npn]{};
  \end{circuitikz}
\end{center}
\begin{center}
  \begin{circuitikz}[american, baseline=(VCC)]
    \draw (0,0) node[npn]{};
  \end{circuitikz}
\end{center}

\end{document}