Abstract: A tachograph comprises a casing (1,2) which houses a speed indicator (4), an odometer (6) and styli (8a, 8b) for respectively recording speed and distance travelled. A stepper motor (22) drives the speed indicator (4) and speed recording stylus (8a). A stepper motor (23) drives the odometer (6) and distance recording stylus (8b). A pulse generator (25) provides an input, proportional to vehicle speed, to a microprocessor (16) which computes speed and distance on the basis of the pulse input and a correction factor (26) relating to vehicle characteristics in order to drive the stepper motors (22,23). The microprocessor (16) is also responsive to a preset maximum top speed reference (27) and a driver selected top speed reference (28) to provide an output to an actuator (30) in order to control the vehicle speed.

Abstract: A tachograph includes stylus recorder (4,5,6) responsive to a signal related to engine speed for recording an indication of the engine speed on a chart (1). The stylus recorder is conditioned to provide a bar trace having different and readily distinguishable levels. Each level represents a threshold of engine speed which indicates that the engine speed is at or below the respective threshold and within a predetermined range. Threshold selector (8 or 9) are provided for adjusting the relationship between the levels and the predetermined thresholds so that the bar trace levels stay substantially the same but represent engine speed thresholds which are adjustably predetermined by the threshold selector.