Pete....just like they did. They assume a deers measurement from top of the back to the belly. Then you get something or make a cut out that's that deep, say 16 inches. You measure off 20, 30 etc. Put some tape on your sight picture. Place a top line(their green) stand at each yardage and draw. Place the top line on the top of your 16 inch target and see where the bottom of the target is on your tape...draw another line..that's that distance. Do it for all the required distances.