I think it calibrate the battery as regarding the task you are running. Forexample if you start some work that need a lot of processor or my be lot of hard disk access or also may be like video brightness then it may use more battery and will show you less and at the time you close it and run some other application that dont need much battery, it may show you more remaining time.
I am not sure what new calibration sony is using for the battery.. but to me it seems like this.