73671719
Jul 13, 1987
Jan 3, 1989
HAND HELD DETECTOR FOR USE IN CONJUNCTION WITH PICTORIAL LEARNING MATERIALS WHICH PROVIDE A FIRST SOUND WHEN ITS READING HEAD IS PRESSED AGAINST A CONDUCTIVE ZONE AND A SECOND DIFFERENT SOUND WHEN THE READING HEAD IS PRESSED AGAINST A NON-CONDUCTIVE ZONE
Electrical and Scientific Apparatus