I've never used a "Square" ruler to square up blocks. I use the center of the block, my regular mat grid and my 5x
24 ruler. For smaller blocks I use a 4x14 ruler. No one told me I needed a square up ruler. LOL. The things you learn to do without tools you don't have. I actually never had any tools other than my rotary cutter, 6x24 ruler and my 18x24 mat until I discovered Jenny... now I have collected some of her templates, two QIAD rulers, a 6 inch square and the five & dime ruler. Just that lone mat and ruler for all the quilts I have made in 20 years!