IBM 5280 User's Setup Procedures page 136

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83. Test the magnetic stripe reader by doing the following:
a. Obtain the magnetic stripe reader test card (part 8331402) from
the envelope in which you found this manual.
Magnetic Stripe Reader
Test Card
Magnetic Stripe
b. Position the magnetic stripe reader so that the wide end of the
slot is to your right.
Magnetic Stripe Reader
c. Place the test card so that the magnetic stripe is at the bottom
and facing you.
d. Run the card through the reader from right to left, with the
bottom of the card at the bottom of the slot.