The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.
It is crucial to know your takeoff roll on those isolated short mountain runways, but those hot high density altitude days on your home runway could also extend your rollout beyond your airplanes performance capabilities. This calculator is designed to provide the data needed to make the right decision prior to departure and should be used as a regular part of preflight planning.