AirDensity for

From Wriston Development:

You can use AirDensity to calculate air density and density altitude based on input of 3 variables: temperature in Fahrenheit, relative humidity as a percentage saturation, and barometric pressure. You can enter each of these in the AirDensity application, then press the "Calculate" button and AirDensity will calculate the air density and density altitude for you.

Alternatively, Applied Data Sciences sells the DaqPod, which can be plugged into your Palm Pilot, then used to aquire the environmental data automatically. To do this, plug the DaqPod into the Palm Pilot, turn on the DaqPod, launch the AirDensity application, and press the "Query DaqPod" button. If you would like to purchase a DaqPod, please contact Applied Data Sciences at http://www.appdatsci.com.

If you're a pilot, you can then use the density altitude calculation to determine the length of runway that you need for liftoff given the weight of your plane, fuel, passengers, and cargo. To do this, please refer to your plane's user's manual.