I bought this refractometer made by AdeAdvancedOptics for $25 the other day and it works great. It came calibrated and was very easy to use. Comes with a hard case, glasses cleaning towel, small screwdriver for calibrating, a pipette and obviously the refractometer. I can now very easily take salinity measurements when ever I want without having to stick anything in the tank and make a mess everywhere. Just two drops of my water and I know the salinity. Very good product and I think it was a good purchase.