This refractometer is hand held with a metal body, flexible eye piece and rubber grip. It features a 0 to 32% Brix scale and from 1.000 to 1.120 on the Specific Gravity Scale with .2% resolution and ATC (Automatic Temperature Compensation). Traditional refractometers without ATC are calibrated to work at 68 degrees Fahrenheit. The ATC function allows you to use the refractometer in an ambient temperature range of 50-86 degrees Fahrenheit (10-30 Celsius.) Because your sample is just one drop, and will quickly adjust to the temperature of the refractometer, the temperature of the sample is irrelevant. This unit also comes with a manual calibration knob that is secured with a lock nut. To calibrate place one drop of distilled water on the testing platform and adjust to zero if necessary.