There is provided with a monitoring method of monitoring plural
apparatuses each having a sensor, including: selecting two or more sample
apparatuses out of the plural apparatuses; calculating averages and
standard deviations of sensor values detected by the sample apparatuses
for each sample apparatus; calculating a confidence interval of the
averages and an average of the standard deviations; and calculating an
average of sensor values detected by an arbitrary apparatus among the
plural apparatuses as an object average and calculating a normal range of
the sensor of the arbitrary apparatus from the object average, the
confidence interval, and the average of the standard deviations.