Growth diagram of monotonic function and reconstruction problem for its original

For monotonic original-functions of real argue the notion diagram (diagram-function) is introduced. The diagram indicates the growth rate of original-function during a certain time interval (which is accepted as the time unit). Many difference-differential equations (DDE) can be presented as the diagram-relation; then the necessary and sufficient conditions for the existence and uniqueness of the solution are revealed. Two examples of such type DDE are considered: (1) Henkin–Polterovich's model of technology diffusion, (2) the model for process of layer-to-layer crystal growth.In itself the “build up” method for reconstruction of original-function which was developed in this article is of interest.