Apple LaserWriter 12/640 PS User Manual
Page 105
105
Installing Options
10
Lift the LaserWriter 12/640 PS, position it directly over the duplex printing unit and gently
lower the printer until it sits evenly on the duplex printing unit.
As you lower the printer, align the corners of the printer directly over those of
the duplex printing unit.
Position the printer
over these three posts.