WeatherCalcHD uses the English measurement system to compute complex Weather equations: Density Altitude, Dew Point, Air Density, Vapor Pressure, Virtual Temperature, Relative Air Density, Saturation Vapor Pressure, and Absolute Air Pressure. The Four Button Control panel operates your WeatherCalcHD. Use the on screen keyboard to enter the Temperature, Barometric Pressure, Humidity and Altitude then Touch the Yellow ENTER Button and notice that the GO Button has turned Green. Touch the GO Button and WeatherCalcHD will then perform the complex algebraic calculations and display the English measurement system solutions. Be sure to HIDE the on screen keyboard to view these results. Activate the HELP screen by first touching the Green HELP Button and then the GO Button. The portrait HELP screen also includes the definitions. WeatherCalcHD directly supports the Internet for the user to access www.weather.com or other websites using the Google search engine. Touch the Green WEB Button and then the GO Button to start the Web. Touch RESET and GO to restart the app. Thank You for your interest in WeatherCalcHD.