Abstract: This invention relates to machines for heating and joining thermoplastic resin sheets and more particularly relates to a portable machine which fuses together the overlapping edges of large stationary sheets as the welding machine travels along the overlapping edges. The machine is moved along the opposed edges of the sheet at a velocity which is changed so that the velocity is substantially proportional to the instantaneous temperature of the heat source. The machine is therefore accelerated or decelerated in accordance with the selected velocity change algorithm which is exponentially in the preferred embodiment.

Abstract: Data processing equipment suitable for recording details of manually connected telephone calls has a plurality of operator stations with keyboards and VDU's connected in groups to operator's control units which respond to keyed instructions to obtain data from peripheral units storing such data and for recording on magnetic tape cartridge the details of the calls. The magnetic tape cartridge recording units are duplicated and the data to be recorded in the two units, which are separately generated and should be the same, are compared with one another and their validity checked. If both data are valid, whether they differ or not, they are recorded. If only one set of data is valid only the valid data are recorded by both recorders. A marker signal may be recorded to indicate that the data recorded may be incorrect.