Griffin has found an Astrolabe in the town libary. He doesn't  know how to use it and he needs our help.
 
Firstly, I needed something to measure so I measured the height of the goal post.

Secondly, I had a friend to help me measure the correct height of the goal post.

Look through the straw to the top of the goal post.  First before we measure we must know that the key angle is 45 degrees. With your string line move backwards and forwards while looking through the straw  until the string line rests on 45 degrees.  Measure from where you are standing to the goal post.  Measure your eye height from the ground and add these two measurements.  The total will be the height of the goal posts.