I have a little gadget called a "quilting guide". It fits through a hole in the back of the thingy that holds the foot and is good up to 3". Got it at Amazon.com - it showed up as a "you might also like this" selection. But ... I'm wondering if you could tape on anything - a craft stick or anything that gave you the right size. I have a friend that marks all the lines with chalk - using 3 yd sticks taped together. Another holds a small clear ruler next to her foot as she sews.