The Extech RF41 measures the freezing point of propylene/ethylene glycol from -50 °C to 0 °C. It also measures the specific gravity of battery acid from 1.11 to 1.30 and provides a quick overview of the battery's state of charge. Only 2 to 3 drops of solution are required for fast and accurate measurements. Automatic temperature compensation ensures repeatable measurements on an easy-to-read scale. Prism and lens are equipped with easy focus adjustment.