Visit the virtual ballooning site linked here to do an experiment and take Temperature and Air pressure readings from different altitudes. After clicking on the link, select "Layers of the Atmosphere".
When you collect data from 4 different balloon launches, come back here to input the data on the blank graph below. Make sure you are collecting data all the way up the graph. You can also watch the video linked here to see how to do the experiment.
Enter the data from your virtual balloon experiment. You don't need to be exact, you can draw points in the approximate location. You can also use the image icon on the left hand side to import images of your data (after you hit edit background).