i just bought a 1/2 inch slotted ruler, first use this morning. needed to cut 1 1/4 (3/4 sashing plus 1/2 SA)
Cut four at 2 1/2 (placement 0, 2.5, 5, 7.5, 10), then moved the ruler & cut them in half. fortunately, there is a 1/4 mark on the outside edge.
1/8" might be handy.
If you do what the others said about cutting 3 3/4, then you could get the one I have. JoAnn's I think $29.99, but got at 1/2 off.