I'll say that for the Protrek,I have found it so easy to calibrate ,just like changing the time on any digital watch,and its as accurate as reasonably expected,especially with regular adjustment at known height and position.One of the studs holding the faceplate has come out but even after endless hours in the kayak,its still waterproof.I wont be attempting to change the battery myself though,as my trusty old G shock leaked like a sieve when I attempted it myself.