I keep an exact count of the number of rounds I put through each of my pistols. When I get a new gun, I open a new sub folder in a main folder & detail round count, magazine count, when & where it was fired, & when I cleaned it afterwards. Since four of my guns were LEO trade ins, I don't really know how many rounds through them they may have. I still track them anyway so at least I'll know how many I've put through them. I also track when I change recoil springs, sights, & any accessories.