On the Quilter's Rule - the little tick marks - they look like hyphens between the solid lines - those indicate the 1/8 inch increments.
Going from one whole inch to another -
1/8
1/4 = 2/8
3/8
4/8 = 2/4 =1/2
5/8
6/8 = 3/4
7/8
8/8 = 4/4 = 2/2 = 1/1 = 1
I am not trying to be a smart alec with the above - I think some of us just did not "get" fractions when they were being taught.
On the ruler with the red markings - the 1/8 inch increments are marked in black along the outer edge - they are between the 1/4 inch markings.