Lay out the blueprint or drawing that you want to read with the architectural ruler.
Locate the scale on the drawing or blueprint. This is typically found on the bottom left-hand side of the page.
Locate the corresponding scale on the architectural ruler, i.e. 1/4" = 1' (1/4 inch = 1 foot).
Align the edge of the ruler (using the side with the "1/4" marking at the end) alongside what you want to measure.
Place the zero at the beginning of what you want to measure and write down the final measurement. You will see that the "2" on the 1/4" ruler means two feet in actual measurement, but on paper is only equivalent to 1/2," or 2 x 1/4."