Pointed the way you have it, the bottom of the moving inside is metric and the top is English measurements. Ignore everything else. Slide the slider back until you can feel the stone comfortably sit in the space then compare the first bottom slash where the slider stopped with the metric line above it and your answer is in mms. If you compare the first bottom slash with the top of the moving middle, and the answer is where they line up in inches. Confused? Buy a battery operated one, and the answers are clear as a bell. If you know the answer in advance, practice with your golden slider until you get those answers!!!!! How didI learn? I took a 7X9 stone, and kept moving things around until I realized I just had to see where the bottom line lined up with the moving track to get a 7, then I swivelled the stone, opened the "jaws" a bit and the first line met the middle slider at the number 9. Have any jeweler show you. They are more than happy to help because you might be a possible new client.