The topic of the auto-zero feature has come up several times both here and or other forums. The following is a brief summary of how it works, when auto-zero is enabled:
When the Vector pedals are woken up (by turning the cranks), the pedals will try to do an auto-zero. This will succeed if the pedals are stationary for the requisite time (usually less than ten seconds) and the bike is reasonably upright. The pedals will also try to do an auto-zero immediately before going to sleep (four minutes after the last pedaling stroke).
Auto-zero will fail if the bike is not upright, if motion was detected, or if the offset shift is too large (which could be caused by a pedal leaning on something).
Auto-zero can be enabled or disabled from an ANT+ bike computer that has the requisite user interface features and sends the standard control messages.
This does not change any of the manual zero features. You can still do a manual static zero calibration at any time, and you can configure many of the current Edge and Forerunner computers to automatically remind you to calibrate, when they connect to a power meter.
Note that the auto zero will only shift the existing zero offsets a limited amount. Thus, when you install the pedals, you should still do a manual zero calibration at that point to get the pedals into a range where the auto zero will track any further changes.