An architectural scale denotes how measurements on an architectural drawing translate to the real lengths of building materials
The small marks in an architectural scale represent the 12 inches in a foot shrunk into a proportionately smaller space -- this is an essential piece of information to interpreting the drawing's scale
Scales can be read from left to right and from right to left, so don't be confused by seeing numbers like 40 and 2 next to each other on the scale
To use a scale, first: set the line you're measuring at the zero mark on the scale. Second: slide your line back into the scale so you can identify how many inches accompany the length of feet measured in step 1.