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.

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[Category GUI] - [Tk syntax help]