Left - Average: An estimate of remaining time based on usage since the phone was unplugged. Some aspects of this may be controlled through the Power Per Percent setting in the Preferences. This setting should get better over time as the app learns more about your device. Note: The Professional and Kindle Fire editions will show an average for time spent active on devices that have no phones (or that are in 'airplane' mode). This allows a more accurate prediction of how much active use you can get out of the device.
Left - Last Xm: An estimate of remaining time based on the device usage over the last X minutes. The maximum X can be is controlled through the Calculate Time Left preference. X may be a small number depending on when statistics were last collected. Statistics aren't collected while the device is not in use, so if you pick up your device after extended sleep time, this number may revert back to 1 and slowly climb as you use the device again.
Left - Talk: An estimate of how much talk time is remaining. Note that this only shows up on devices with phones.
Time to Full: When charging, this represents how long it will take to fully charge the device. Charge time can vary based on charger type (USB vs A/C) and usage of the device while it's charging.
Battery Usage - X% (TIME): X shows the percent of battery consumed based on your time reference (by default since you last unplugged the phone). The TIME section shows the amount of elapsed time since the time reference (typically how long since you unplugged your phone). All statistics have been gathered since the time reference