This is a great tool: [a] it illustrates the orbits of the GPS satellites, [b] gives their geocentric coordinates and [c] orbital parameters. I certainly will use it in the classroom to demonstrate underlying concepts of the GPS system in introductory GIS/Stats courses. It runs very stable on my iPad (3rd generation with GPS chip). However, to make P-Track fully functional as a teaching tool, it must provide some hidden information:[a] a down-loadable log-file file over a reasonable time frame should capture [b] the displayed data for all GPS satellites and [c] some additional data such as the satellites and the receiver times. This would allow demonstrating simple to advanced stochastic GPS calculations and error assessments. If you have two GPS equipped iPads, you could even start playing around with differential correction.