I was using the side of 1/4" foot and thought when I measured it that all was fine but things weren't and I've had one of these for some time and now have blue painter's tape marking the distance.
http://www.amazon.com/Dritz-Quilting...ef=pd_sim_ac_1 Nancy's Notions also has a gauge that does the same thing. Good luck. I now know to use the same thing to sew every block instead of the foot one time and the tape another.