I was just working on a project which I had measured with my measuring tape. I grabbed a quilting ruler because I needed a straight edge and noticed the measurement was 13″ instead of 13 3/8″. I checked against another ruler and sure enough, my measuring tape has shrunk. So make sure you check your measuring tapes every once in awhile to see if they are still accurate.
On the bright side, maybe I am not *quite* as fat as I thought I was because I measured myself with a shrunken tape!