Creating a square tool required some sort of rule or trick: the 3-4-5 rule, your solution, or blind luck. Creating a level meant easily deducing a straight line

Creating a square tool required some sort of rule or trick: the 3-4-5 rule, your solution, or blind luck. Creating a level meant easily deducing a straight line from the surface of a liquid, which became known as a "spirit level". The 3-4-5 rule was also easy to use with tools such as calipers, protractors, and lengths of cord. Also, from the standpoint of working in enclosed spaces, the 3-4-5 rule takes about half the width of your solution.