Most refractometers have a scale division that is equivalent to water. in the case of a Brix refractometer, it is 0.0 Brix, and on the Glycol & Battery Tester, it is +32°F (0°C). This is the reading you should get when testing water at room temperature. If the reading for water does not equal one of the above values, then you need to recalibrate your instrument.
For more information about our analog refractometers, please see the following page: How to Use a Traditional Handheld Refractometer.