This function returns the system's dialog base units, which are the average width and height of characters in the system font.
long GetDialogBaseUnits( void )
The function returns the dialog base units. The low-order word of the return value contains the horizontal dialog box base unit, and the high-order word contains the vertical dialog box base unit.
The horizontal base unit returned by GetDialogBaseUnits is equal to the average width, in pixels, of the characters in the system font; the vertical base unit is equal to the height, in pixels, of the font.
The system font is used only if the dialog box template fails to specify a font. Most dialog box templates specify a font; as a result, this function is not useful for most dialog boxes.