The present invention is an interferometer sensor which uses frequency modulated coherent electromagnetic radiation to noncontact measure the displacement of moving targets with high precision. Because foot propelled scooter is put into motion by using foot oscillation, thus creating an effect of exercise and frolic to the rider. The data elements encode data values by pulse position modulation, which facilitates the low-pass filtering. The grooves have a maximum depth less than the diaphragm thickness, and a floor at the maximum depth, forming first and second frangible webs between each groove floor and the secondary surface.