I've only had mine for a year. I typically check the accuracy the first time a get a new (to me) watch. I had tested my Mark XVIII LPP to be ~+4 sec. after the first 24 hours.
Maybe a few weeks later when I left the watch unworn and set the time, I checked again and it was ~+7 sec after 24 hrs.
I hadn't really checked the accuracy after that, but I feel it's hovered around the +6-7 sec per day.
I always do crown up by default (for no good reason), btw.
I really should get myself to test in different orientations, to see if I can create a habit to keep the accuracy even tighter!
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