Abstract: A calculator for computing the estimated time of arrival of a vehicle or the like at a desired destination. The calculator, under control of a microprocessor and related interfacing devices, computes and periodically updates the estimated time of arrival at the destination from information reflecting present chronological time, the total estimated distance and the desired average speed to be travelled to the destination, and the actual distance travelled by the vehicle. The information resulting from the microprocessor's computations is visually displayed together with the present chronological time. The calculator may also be provided with warning sensors to provide an indication when a predetermined maximum speed has been exceeded. In an alternate mode, the calculator may be caused to function as a standard four function calculator, without affecting data previously stored in the estimated time of arrival mode.