According to the old nursery rhyme, there once was a crooked man who, along with his crooked cat and a crooked mouse, lived in a little crooked house. Obviously, the crew that built their place worked without a square, a level, or a plumb line.
The truth is that the importance of straight lines and regular angles was recognized a very long time ago by the ancient Greeks, and even earlier by Egyptian builders. In this country, all the early builders’ books, from the eighteenth century onward, devoted more pages to geometry and trigonometry than to tool techniques. That’s because any object or building is made or built by connecting points (to form lines); by combining lines (to establish two-dimensional shapes); and then by adding the third dimension to create volume. Thus, accurately drawn lines and angles are the essence of the building process.
There are tools that tell us what is “true” (that is, level or square) and what is not. These include squares, which are used to check the trueness of angles (usually 90-degree angles); spirit or “bubble” levels that advise us when we’re on the level; and plumb lines, which help us keep our work standing straight.
Each of these tools also has other uses. Many squares, for example, have inches and fractions of an inch marked on their blades so that they can be used as rules. Levels are handy as straightedges, too. But, at bottom, these are the tools that will keep you from being known as the person who lives in the little crooked house that’s full of little crooked objects.