Squaring up is very different from just plain measuring. On this ruler, the numbering goes from one corner along two sides. It does not go both left and right.
The entire ruler is gridded using the same symbols as Marti Michell's two larger rulers, but in addition, there is a shadow that follows every inch mark, turns a corner and connects to make seeing squares very easy.
Right-handers generally put the focal corner in the upper right while left-handed cutters will position and measure from the upper left.
When those two exposed edges are trimmed, the fabric piece is rotated so that the trimmed sides line up with the correct measurement and the untrimmed sides are ready to be perfected.
There is one 45 degree diagonal line. Many people like to use that when they square up half-square triangle pairs.
Four distinct line styles for 1/8", 1/4", 1/2" and 1" increments.
Every line has spaces so you can align the cut edges of the fabric with the line, no one one or other side of the line.
The centre circle marks the exact center of an 8.5" cut square or 8" finished square. The extra shadow line creates a 4" square in the center of the 8" finished square for centering a large fabric motif.
The last 1/4" on two sides is used to check the accuracy of seam allowances.