To evaluate contact instability and weakness, we need to decompose into and . To do so, we apply low- and high-pass filters to . Because is white noise, its low-pass filter output is very small. On the other hand, because originates from body motion, and most of its spectrum is in the low-frequency region, this component is not significantly affected by the low-pass filter. As a result, the low-pass filter output of can be used as . On the other hand, the high-pass filter output of mainly consists of , and it includes only a small baseline fluctuation. Although the apparent noise may change according to this fluctuation, it is also filtered out by a high-pass filter. Therefore, we can use the high-pass filter output as .