What does the "Power Logging" setting in iOS4 do

I noticed 开发者_如何学JAVAa new setting screeen on the iPhone since iOS4: Settings -> Developer (just below iPod, Photos, Store) -> Power -> Logging.

Does anyone know what this does? I could not find anything about it in the documentation or on the net.

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This is part of the newest version of Instruments and iOS4. You can record your power usage while your phone is on, running apps, doing whatever you please. You can then load this log into Instruments and see various events and the powerlevels they required. This is great for optimizing games and other high power usage applications.

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Is this removed in iOS 4.1? My iPhone 3Gs is developer-sanctioned, and I'm sure I saw the Settings > Developer menu in 4.0.1...