I’ve used a bunch of different meters over the years and have come to one conclusion. Trash. When a bunch of replacement Bluelab Guardian probes were bad brand new, I threw it all away. They’ll lie (even after calibration) after about 6 months to a year. Test drops have never failed me. Thankfully I’ve always had them to test against digital meters.

5 years? I don’t believe that at all. They don’t last more than a year even if maintained properly. It’s lying to you at this point.