[DrHank]

Sorry that I wasn't able to respond sooner Melanie. Steve's post sums it up. There are many calibration solutions on the market. The point though is to calibrate any refractometer as nearly as possible to 35ppm at the optimal temperature. Slight inaccuracy would rarely cause any problem because there are natural fluctuations that occur. The time that accuracy really becomes a major factor is with hyposalinity treatment.

Also, I don't use any calibration solution. My 30 year old bulb hydrometer still works great so I haven't found the need to purchase a refractometer. I have used refractometers many times but my old hydrometer is even easier to read and consistently nearly as accurate.