Calibrate your screen
There are many different shapes and sizes of computer monitors, so in order to show you life-size images, we first
need to calibrate your monitor. Luckily this is really easy. If you have more than one monitor of different sizes you'll need to re-calibrate each time you use gemdat on a different display, sorry!
Step 1 - hold up a standard size credit or store card to the top left corner of the window below, and click the mouse where the
bottom right of the card would be if the corner was not curved.