Tikz: Polar coordinates with arc

Question

I am trying to draw the arc of a circle that starts horizontally going to the right and ends vertically going upward, like in the fourth quadrant of the graph of a circle centered on the origin. However, I get the following instead:

Why does this happen? In the documentation for canvas polar coordinates, it's said that an angle of zero degrees is to the right, not upward.

\documentclass{standalone}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \draw[help lines] (0cm,0cm) grid (3cm,2cm);
    \draw (1,0) arc[start angle=0, end angle=90, radius=1cm];
\end{tikzpicture}

\end{document}

Answer 1

The arc you are describing can be obtained with (modulo start position)

\documentclass{standalone}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \draw[help lines] (0cm,0cm) grid (3cm,2cm);
    \draw (1,0) arc[start angle=-90, end angle=0, radius=1cm];
\end{tikzpicture}

\end{document}

Why? If you want to start out going right, you need to be at the lowest point of the circle, which has the polar angle -90. The vertical stretches have polar angles 0 mod 180, so your end angle needs to be 0 or -180.