Download PDF 4055906 US Patent References: 3735503PROGRAMMED INSTRUCTIONAL SYSTEM1973-05-29Dow et al.35/9A 3689930OPINION SAMPLING APPARATUS1972-09-05Strickland35/8R 3629956TEACHING AND GAME PLAYING MACHINE1971-12-28Thomas et al.35/9A 3628255APPARATUS FOR TEACHING OR TESTING AN APPLICANT1971-12-21Go...