The second STAR-CCM+ Macro Competition took place at the 2016 STAR Global Conference in Prague. That year the competition was part of the Java Lecture. During such lecture, a set of macros and a simulation were used. At the end of the lecture, the macro competition started by posing a question to the participants related to the simulation. In this video, you see the proposed solution that is implemented through a negative feedback loop. The attached pdf file shows you that this is equivalent to a pure integral controller. The pdf also shows how to implement full PID controllers without the need to resort to derivative or integral calculations. The attached java file is the STAR-CCM+ macro as shown in the video (Do Note: use double precision in STAR-CCM+ when testing it).