This is the correct setup of a steeltip board . The red line marks the throwing line.
Height is measured from the floor to the center of the bull's eye.
If you ever play in Europe you will notice that there are softtip machines with boards sized like in steeltip. A line on the floor you must not overstep when throwing. If you want to set up a decent throwing place you should implement an oche. You will find it in most better pubs and at all tournaments that have some importance. It just makes overstepping the throwing line impossible, leaving no room for tiresome dispute.