I asked the same question not so long ago: http://slashdot.org/submission/2004807/ask-slashdot-how-do-you-go-about-testing-a-storage-medium sadly the comments with all the helpful messages in seem to have disappeared.

This appeared on my android device a good few weeks ago now right next to my handsets "camera" icon in the app draw. I even remember thinking to myself "oh for facebooks sake, thats confusing!" a few day's later the thing changed and a little facebook "F" icon appeared like an icon overlay on the main icon

err actually no that is not right. The GPS satellites are regularly maintained by the US military and satellites updated and checked often by their personnel. pretty much all mobile handsets set their time from the current local cell.