This Mason's Hygrometer (wet and dry bulb thermometer) is wall-mounted and comprised of two identical dual-scale thermometers. One has a dry bulb while the other is kept wet via connection to a water reservoir. Relative humidity is calculated from the difference in readings between the two thermometers. Dual scale ranges are -10°C to 50°C and 20°F to 120°F. The instrument measures 11.5 inches long, 3 inches wide, and 0.5 inches thick. Suitable for meteorology instruction, weather monitoring, and environmental science classrooms.