I've also caught my tenth grain weight out of place but since I charge all cases with powder before seating bullets, it wasn't hard to go back and re-weigh the previous few charges until I was certain of when I bumped it out of place. I use two separate loading trays and transfer the cases from one to the other at each step so none get missed or duplicated. After that incident, I try to make a point of checking the position of scale weights every weigh, again after every ten, and double check at the end before seating any bullets. I try to build error out of the method as much as possible, but even then, all it takes is one moment of inattention. Good reminder.