I found the hidden screens within ten minutes of powering it on the first time. Upon phoning Magellan and inquiring what these screens were, they said it was a hidden function for technicians to diagnose problems and also mentioned that I could mess up my unit by mucking with it (frankly, I don't believe I could mess it up, but I'm bold like that). There are many screens, all with data that seems to be obtained from the satellites, but I'm uncertain of the true orgin of the data, or its meaning.
As for holding down buttons while powering on, I'll have to try that.