I agree with everyone who's posted. Here's a tutorial on how to check your seam and figure out where the sweet spot is on YOUR machine. I would take an hour or so and follow the tutorial and figure out where the 'scant' quarter inch is, then use one of the methods above to mark it. One method not mentioned is use a stack of post it notes. When the sticky stops holding, take the bottom sheet off & you've got a whole new adhesive.
http://www.quiltingboard.com/t-89997-1.htm
It's also good to recheck if you switch to thicker or thinner fabric or thread, but usually once you've taken the time to figure it out, your good to go. Cheaper than getting a whole new machine!!!!