Epson EQUITY 386SX/16 PLUS - Manual (Page 114)

6.
5-30
The math coprocessor also has a notch in one corner,
marked by a dot, as shown below.
notch
A80370X-16
SX106
L9450188
1986
V
Align the notched corner of the coprocessor with the
notched corner of its socket. The notched sides must be
aligned for the coprocessor to operate properly, so be sure
its position is correct before you go to the next step.
Caution
If you insert the math coprocessor in the wrong
position, you could permanently damage it and
destroy the components on the main system board.
Gently push the coprocessor into the socket, pressing
evenly on all sides, as shown below.
Installing and Removing Options