OK, so the point of this project is to build a launching pad for a spring launcher that can launch a spring (that will be provided on the day of the launch) anywhere in the the classroom. My class room is about 4m long, 5m or 6m wide and about 2m or 2.5m high, my teacher said the box that you have to get the spring into can be anywhere in the room so you have to do the calculations, calibration and all other preparation before hand.

These are the calculations I've done, can somebody check them over if they look right? There might be some algebra mistakes.

My design concept is pretty simple, two wooden blocks connected by a door hinge and a protractor attached to measure the angle.I have a ruler on the top block to measure how much I have to stretch the spring.

Does anybody know a good way to fix the angle, once I have it lined up?

I haven't started building it