yeah and that is why your going to break your leg. there is a few things you have to do. first off you can't just line it up to the back of the boot, there is this thing called forward pressure...very critical. also if your bindings have it, there is toe height adj, adn the toe wing adj..mainly salomon. adn yes there is a chart to go by to set your din which considers several factors; your boot sole length, weight, height, skier type, adn age. also if they are used bindings it is smart to take them in to have them torque tested which to put in laymans terms determines if the bindings are going to release when they are supposed to. so yes take them to a shop.
adn good luck.
fuk that