Doesn't work on my Retina MBP either, but it works on a connected regular res monitor. The problem appears to be that it maps 2x pixels to "normal" 1x pixels a

Doesn't work on my Retina MBP either, but it works on a connected regular res monitor. The problem appears to be that it maps 2x pixels to "normal" 1x pixels as output. So all the measurements are scaled up 200%, with the top left corner as the origin.