IBM ThinkPad Dock User Manual page 8

(6) By pressing the release button, you can detach the computer from the
ThinkPad Dock. The button cannot be pressed when the docking indicator (3)
is on.
(7) The docking connector is where you attach your ThinkPad computer.
ThinkPad Dock II
(1) The docking indicator turns on when the ThinkPad Dock II is in use. When
the indicator is on, you cannot detach your computer by pressing the pop-up
eject button.
(2) The power switch turns the computer on and off.
(3) By pressing the pop-up eject button, you can tell the operating system to
get ready for undocking. (You can do the same by selecting Eject PC in the
start menu of your computer.) When the docking indicator turns off and the
button pops up, press the button again. You can now detach the computer
from the ThinkPad Dock II.
(4) The system lock key is for locking the pop-up eject button (3).
(5) The docking connector is where you attach your ThinkPad computer.
(6) Slide the sliding adjuster forward when attaching your ThinkPad computer
to the ThinkPad Dock II .
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ThinkPad Dock, ThinkPad Dock II: User's Guide