The Extech RF41 monitors the freezing points of propylene and ethylene glycol from -50°C to 0°C. It also monitors the specific gravity of battery acid (1.11 to 1.30) and gives a quick reference for battery charge status. For quick and precise readings, only a few drops of solution are required. The automatic temperature correction yields reproducible results on an easy-to-read scale. Prism and lens have a simple focus adjustment. The set includes a carrying case and a calibrating screwdriver.