I haven't read all of the responses so hope I'm not repeating ; I would get a 1/4" foot AND use a stack of post-its (I do mean a stack at least 1/4" high). I use Olfa cutting mats and rulers and have found I need to measure from the fat lines. Make sure your rulers and mats measurements are the same; using the same brand is a help, if not possible lay your ruler on your mat and see if they match in inches. If your machine has the option of moving the needle to the right or left, do some practice seams and see what needle setting gives you the accurate 1/4". I have to move my needle over 2 positions to the right even using the 1/4" foot.