Supplement the existing design with more design details

The first design often did not include all of the details necessary to code and test the entire program.

Once you have coded and successfully tested the design at its current level of design detail

• The next step is to go back to the top and supplement the existing design with more design details.

Sometimes for very complex programs, it is necessary to repeat this cycle several times. 

This cycle is what is commonly referred to as the program development cycle.