1. A method of estimating a fracture point in a large scale network for the distribution of water, gas, oil or electrical power provided therein with joints and with a fracture monitoring system, comprising the steps of (a) initially selecting a set of suspected abnormal joints in the network; (b) successively applying through apparatus associated with the system a set of estimating rules which comprise (1) calculation of an unknown pressure at a joint of a branch in which flow rate is known and pressure in another joint of the branch is known, (2) calculation of a flow rate on a branch when pressure at joints of the branch are known, (3) calculation of the flow rate in a branch among a plurality of branches adjacent to a joint not belonging to the selected set of suspected abnormal joints, (4) calculation of flow rates in a path having no branches therealong where pressures at the ends of the path are known and joints between joints at the end of the path do not belong to the selected set of suspected abnormal joints, and (5) when two or more pressures of the joints belonging to the suspected set are known, searching a joint of the suspected set in which the pressure drop reaches a maximum, (c) preparing through the apparatus a new set of suspected joints by removing from the new set the joints of the initial suspected set at which the pressure drops are known other than the joint exhibiting the maximum pressure drop, from the initial set of suspected abnormal joints, searching the joints along branches adjacent the joint of maximum pressure drop until a joint not belonging to the initial set of suspected abnormal joints is found, and updating the definition of a set of suspected abnormal joints with the use of set of joints obtained during said searching, and (d) successively reducing the number of suspected abnormal joints in the selected set until the fracture point is located.