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.
- iThe 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.