A hand-held calculator programmed to teach mathematics in a manner which emulates traditional step-by-step teacher-student teaching methods and shows the important intermediate steps. The first seal ring is of a generally annular shape and defining radial and circumferential directions. With a squaring circuit at the output terminal of the detector circuit and a narrow-band filter at the output of the squaring circuit, the clock signals at the predetermined clock signal rate are recovered. Another aspect pertains to an improved training sequence wherein pairs of identical symbols are transmitted by a transmitter. Each of the preparation steps are displayed to the user on the flexible horizontal surface display.