Many people tend to mix up car vibrations from the road with the vibration of the upholstery. To show their difference, we show graphs (top) when an iPhone was set on the dashboard of a car and those (bottom) when it was set, covered by a floor mat, on the floor of the same car.。

The car was driven through the same corner with the same speed in both cases. Compared with the lower graphs, the upper graphs are mostly jagged. This is the influence of the vibration of the upholstery (allowing a room for improvement).