Geez I maintained the saws for 3 tree crews back in the day and we never had this much debate over chains stretching. I don't think we ever had one that didn't have more slack in the chain at the end of the day than when you started. Hit all kinds of nails, rocks, fences, you name it cutting down trees at residential locations, so we went through a lot of chains. All we ever did was snug em up a little as needed at the next job or the next day once they were cool, which was only if they were pretty loose because the guys were so busy.