Check out the link above for a useful product for setting trims in a fly-house. While normally used for surveying, it is useful in theatre. The one shown goes to 25'. You can extend the top potion of the rod and at eye level a window will display the measurement that the total length of rod is at. So if you need a drop to be flown to 23'-6” you would extend the rod to that measurement and then compare that to the leveling rod. You can also use it to check the trim on something that is already flown to to check sightlines.