I buy these for work so this review may not have been verified. We have 7 of them running at the same time and most of them are used daily in business operations. We use it to measure free chlorine in the range of 2-6 ppm. They're pretty easy to use and I love them. They also seem to be fairly accurate and consistent. (Free Cl) They seem to last quite a while. In the five years it's been part of my job, I've had to replace or repair a few. However, I don't think it's a bad thing considering how much we use them. I've never had any waterproofing issues, usually a bad battery connection that I can fix by soldering, or circuitry issues that need replacing. I would say I replace them about once a year so they will probably last 5-10 years with daily use.