A grinding device for the flats of a card comprises elastically bendable elements which enter between the clothing points, brush over the side flanks of the points and thereby grind the points. An apparatus is disclosed for recording image or other data in real time. A low-melting metal coating 13 is formed on contact 12 and two board pieces 2a, 2b are pressed against each other under heating with contacts 12a, 12b thereof being in contact with each other so that thermoplastic resin films 10a, 10b soften to adhere board pieces 2a, 2b to each other and low-melting metal coatings 13a, 13b melt and then solidify to connect contacts 12a, 12b to each other. The resonating speaker is assembled onto a bottom of the housing and the resonating speaker contacts the resonating surface. The detection signal is compared to a predetermined threshold. 1 when A is O, then n is 2 or 3 when A is 2then n is 1 or 2.