the add a 1/4 is for paper piecing, there is also an add 1/8 for mini paper piecing. these come in 6 & 12" and have a small lip that fits over the edge of your paper piece. there is a 1/4" ruler that is a 1/4" square for adding a 1/4" to anything you are making. If you are making court house steps, it seems any ruler could be used just add a 1/4 to your measurements.