Once all the connections are in place, the display will start displaying a series of numbers from 0 to 9999 in a quick increasing order. You can now slowly see how the right most number gets displayed first. Once the count increases beyond 9 i.e., the units place is crossed, the second last digit, 10s place number, appears. Later when the count crosses 99, the 100s place digit appears. Lastly,  when the count goes beyond 999, the 1000s place digit appears. Thus, all the 4 7-segment display digits are visible one after the other.