This circuit can be used for many purposes. Applications ranging from simple bottles in the belt, display a number in the queue physician practices, the timer display for competition pool, until a little complicated to show the amount of rotation in one minute lap machine.
Similarly if there is a logic transition on the 0 to 1 DN pin (pin 4), the BCD output down 1 digit. It is a good idea if you explained a little about the rules of the BCD, as there is on the table. This is shown in the table 4-bit binary code QD .. QA-me representasikan code decimal from 0 to 9.