For the price, I think it's a good product. When you receive it, normally, it is already calibrated and thus ready to use. The instruction is in English but frankly with school English and a little common sense, it's OK. The bags come with 2, are solutions to calibrate the device. In short, it works great. I use it for the pool and the pH is very accurate and just about 0.1. You find the same product at some piscinist for 53 euros!