The Extech RF41 is a portable analog refractometer designed to measure the freeze point of propylene and ethylene glycol-based coolants in degrees Celsius, as well as the specific gravity of battery acid. It features Automatic Temperature Compensation (ATC) for accurate readings between 10°C and 30°C (50°F to 86°F). Requiring only 2–3 drops of sample, the RF41 provides clear, dual-scale optical readings and is ideal for automotive, industrial maintenance, and battery service applications. The unit includes a protective carrying case, calibration screwdriver, and calibration solution.