Hi Emad, You work with a set of AXIS lines that cross each other and create a fixed point in the centre of the image. From there you make all of your measurements. Watch this video to see haw its done at the 1min mark ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-31HjlBuT-fs.html Hope this helps
