Review on 🔵 Ultimate Accuracy VIVOSUN TDS Tester 3-in-1: TDS EC & Temperature Meter - High Precision Digital Water Quality Analysis (Blue) by Emily Waffles

Because these are "cheap" pens, I bought two. Mainly because your counter never dies at an opportune time. In this case it was good that I bought two. The first showed 44.9F. Press the button to switch to Celsius scale and it will show 23.0c. Hmmm? So I change it to another one as the second device seems to be reading accurately. The instructions state that the device can be calibrated. However, they do not provide any instructions on how to perform the calibration. It also doesn't specify which calibration solution to use. It says it's calibrated at the factory. All in all a decent device. Unfortunately, new means new doesn't work. Make sure you test it somehow. Even a replacement for the shelf ;)