i have the 517. It's just like a 516 but uses AA batt., and has all the good features that remedy some of the shortcomings that users pointed out: 7mm raised base, buttons relocated to the side, and better waterproof feature (well, it's not like I'll go swim or perform an underwater Op with it

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Plus the 517 looks better than the orig. AA batt. 512 model. Somehow the batt. compartment 512 looks like a duck's beak to me and i can't stand it