The system displayed here is a Gill MetPakPro, and measures Temperature, Humidity, Pressure, Wind Speed and Direction. Air Temperature is displayed in degrees Celsius. Barometric, or Atmospheric Pressure is the force exerted on the surface of the sensor by the air above the surface in the atmosphere of Earth. The data is given in a unit called hectoPascals, which is equivalent to the more common term, millibars. At sealevel, the barometric pressure is typically around 1013 hPA (or 1013 millibars). Severe storms often bring a lower pressure; for example a tropical cyclone, tornado, or waterspout might have a pressure of 870 mbars. It is therefore important to watch the Pressure reading for incoming storms.
Relative Humidity is described as a percentage; it is the ratio of the amount of water vapor the atmosphere can hold at its specific temperature and pressure to the amount of water vapor that is actually in the air. Humans are sensitive to relative humidity, because it affects the rate of evaporative cooling (perspiration) that the body can use to cool itself. A high humidity slows the rate at which perspiration evaporates from the skin, thus slowing the rate that the human body can cool itself. The same principle can be applied to vehicles, such as ships.