Ambient Weather WM-4 Handheld Weather Station w/Windspeed, Direction, Temperature, Humidity, Compass, Dew Point, Comfort Index, Psychrometer The Ambient Weather WM-4 is a comprehensive handheld weather station, directional compass, heat index monitor and psychrometer, all in one compact, portable, rugged package. The WM-4 measures wind speed, wind direction, temperature, relative humidity and compass direction, and calculates wind gust, dew point, wet bulb and dry bulb temperature, Delta T, wind chill and heat index. It has a USA-made fluxgate compass for precise digital wind direction measurement, and it can also be used to calculate crosswind & head/tail wind readings with the built in wind vane. The WM-4 measures wind speed, wind direction, temperature, relative humidity and compass direction, and calculates wind gust, dew point, wet bulb and dry bulb temperature, Delta T, wind chill and heat index. The jack knife case design protects the unit, and allows you to hold the case while taking precise temperature measurements, avoiding false readings from your hand temperature.