90° angles
The angle most often used in the trades is the 90° angle.
It may help to understand why this is so.
When two straight lines cross, four angles are created.
Those four angles always add up to 360° .
The major lines of the compass are two straight
lines which cross each other at 90° angles.
Most plants and factories are said to be built along
the major lines of the compass.
When lines cross, the only time all four of the angles
created are equal to each other is when each angle is
a 90° angle. A 90° angle is called a right angle.
Seeing is Believing: Fractions of the Ruler
