Bought this off of E Bay to replace my old one that is failing, after many years. Forget ordering one from Amazon, waited two months, abd never received it. BTW, before someone attacks me. I have a head injury, and cannot use a a Refractometer, even with my corrective glasses.
I use one all the time, mostly for mixing water. The number indicated rarely is accurate but I test it against a refractometer periodically and just mark/remember the target. As long as it’s repeatable who cares!