An apparatus is disclosed comprising a suite of sensors for measuring instant static and dynamic pressure and the speed and acceleration of a vehicle, such as a bicycle. A microprocessor receives data from the sensors and calculates power expended by the rider or other power source by finding the total of all forces impinging upon the vehicle and rider, thereafter multiplying by the speed of the ground vehicle. In some embodiments accuracy is improved by calibration techniques, user input of data, or temperature compensation of certain factors. Other data, such as wind speed, distance traveled, altitude, or surface grade may be presented to the user. In one embodiment data is stored for later analysis.