How do you measure a right-angle on the ground?

Answer 1

You can do it the way the Egyptians did it, by measuring out a Pythagorean triangle. I would suggest a triangle with sides of length 3, 4 and 5. You have probably noticed that I didn't mention units of length.

If you are building a huge thing, such as a right-angled road intersection then you could make a triangle with sides 3 kilometres, 4 kilometres and 5 kilometres. If you a building something in a small factory then metre units might be what you would need.

You will find that the right angle is formed between the 3 and 4 sides of the triangle. You therefore begin by measuring out the 4 unit side starting from the point where you want the angle to be, along one side of that angle. Then you go back to the point where the angle is to form and make an arc with a radius of 3 units straight along the ground from the side that you've just measured. No go to the far end of the 4 unit line and from there make another arc of radius 5 units that crosses the first arc. Join the point of intersection of the two arcs to the nearest point of the original 4-unit side to get your right angle.