An information processing system includes a sensor node and a server. The sensor node obtains acceleration data and transmits the data to the server. The server obtains and records the number of zero crossings from the acceleration data. The server obtains and records the frequency distribution of the number of zero crossings. The server obtains one or more of the following: the slope of the approximate line of the distribution; the linearity of the distribution; the inflection point; the slope of the approximate line in the zero crossing range below the inflection point; the slope of the approximate line in the zero crossing range above the inflection point; the linearity of the distribution in the zero crossing range below the inflection point; and the linearity of the distribution in the zero crossing range above the inflection point. Then, the server records the obtained value.