Some of our customers add various guidelines that provide a double check that everything is in the right spot. For example, for two holes that need to be 10 inches apart, they draw a comment line between the hole centers and leave the line in the drawing. They check that the comment line is 10 inches and that the circle centers align with the line end points. Though not necessary, such comment lines can add a level of comfort since ems drawings are normally not dimensioned.