The Chatsworth OMR1000 is a popular optical mark card reader that is
normally connected to an Apple IIe. It is also compatible with the Apple IIGS,
but with one precaution.
The OMR software defaults the slot for the controller card to slot 4. On
the Apple IIGS, slot 4 defaults to MOUSE. Before using the OMR1000 with the
IIGS, use the Apple IIGS control panel to change Slot 4 for "Your Card".