Updated 2011-09-20 03:15:38 by RLE

These are the valid screen distances, according to the man page for Tk_GetPixelsFromObj, Tk_GetPixels, Tk_GetMMFromObj, Tk_GetScreenMM:
<none>
The number specifies a distance in pixels.
c
The number specifies a distance in centimeters on the screen.
i
The number specifies a distance in inches on the screen.
m
The number specifies a distance in millimeters on the screen.
p
The number specifies a distance in printer's points (1/72 inch) on the screen.

The above are all suffixes to floating-point numbers. Thus, 5 is five pixels, 5c is five centimetres, and so on.