G-Shocks are all rated to be accurate within 15 seconds per month, and each one will vary slightly in how many seconds it loses or gains over time. SopheNic wasn't happy with the accuracy of his G-9000 Mudman. So he cracked it open and adjusted the timing inside. There's a tiny screw that can be turned to speed up slow down the quartz in very small increments. Take a look and see if you'd be willing to do it yourself.

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Inside view of a Mudman