IBM Personal Computer AT Manual To Operations page 22

5
Turn your display contrast and brightness
controls clockwise.
(If
your display has a Power
control, turn the display on.)
6
Turn your system unit's power on.
Note: Each time you turn your system unit
on it does a Power-On Self Test (POST)
which completes in 13 to 90 seconds.
--"
System Unit
Power Switch
1-10 System Unit