The maximum and minimum gradients are obtained from the gradients between the two neighbouring survey points in eight directions. The gradient shown in this Yearbook represents the maximum gradient. Accordingly, private lands under the statutory tax exemption are included, but exclude following lands, which are exempted from the fixed asset tax, such as lands owned by the government or the local public bodies, lands for official or public use, graveyards, roads, irrigation channels, sewerage, reservoirs, reserved forests, private school sites, compounds of religious bodies, etc. Observations of atmospheric pressure, air temperature, relative humidity, etc. are made at the scheduled times of a day, but the frequency of observation varies depending on the observation station and the object. Atmospheric pressure, temperature and relative humidity are observed 24 times a day.
Arithmetic average is used for the calculation.
The normal annual values are calculated according to the widely used international practice by taking average of 30 years consisting of three decades on the Gregorian calendar. The average normal values now in use are the average of the 30-year period from 1961 to 1990. During this period the frequency of measurement differed from the one currently in use. Duration of sunshine Data are based on the rotating mirror sunshine recorder, indicating total hours the sun shines on the ground. Maximum precipitation Represents both the maximum value of daily precipitation and the maximum value of hourly precipitation in a day.