I was paging through my copy of Sharp's "Complete Guide to Handloading" and noticed something I'm unfamiliar with, seating depth listed in thousandths of an inch. Example; 45 Colt, 255 Lyman bullet with a seating depth of .425". I assume that is the distance from the case mouth to the base of the bullet, but not sure. The load data is from the mid thirties and this stat for seating is used on all calibers and bullets listed in the text. So, any of the old timers have an explanation, that know for sure how this method is used, or what the dimension means?