Two canopies out usually happens if the AAD fired during your main...
Spot Assist is a mobile application to visualize different stages of your jump
How does it look
It also has additional features, like Simulator and Cutaway Finder. Simulator might be very useful to see the effect of wind on your skydive.
How does it work
Honestly – it is kind of magic, just look at this
If you still insist – it is plotted based on the current weather data at your dropzone. Not enough? Ok, all the details about the math behind it are described at the Spot Assist website: Flying Formula
Also, the website contains pretty nice write-up about the app What is Spot Assist