If you mean via DDC then I guess this should work in most places, but for
whatever reason it does not work here :( In particular, xdpyinfo says:
screen #0:
dimensions: 1024x768 pixels (321x241 millimeters)
resolution: 81x81 dots per inch
So it appears to know the screen size (I measured with a ruler and
321x241 is right), but it gets the DPI too small anyway. At 81 dpi the
text is hardly readable.
But:
1024/321*25.4 = 81.026
768/241*25.4 = 80.943
Seems to me X has it very right. That Windows usually doesn't care about
real resolutions and instead fudges with it (consider the Large Font setting
in the Display Control Panel) is probably another issue. Or the metrics this
function requires are not dots per inch but something else.
Rolf Kalbermatter