Emacs uses the same units as @code{xterm} does to interpret the geometry.
The @var{width} and @var{height} are measured in characters, so a large font
-creates a larger frame than a small font. The @var{xoffset}
-and @var{yoffset} are measured in pixels.
+creates a larger frame than a small font. (If you specify a proportional
+font, Emacs uses its maximum bounds width as the width unit.) The
+@var{xoffset} and @var{yoffset} are measured in pixels.
Since the mode line and the echo area occupy the last 2 lines of the
frame, the height of the initial text window is 2 less than the height