The idea of digital signal filtering has been widely discussed on forum topics about building trading systems. And it would be imprudent not to create a standard code of digital filters in MQL5. In this article the author describes the transformation of simple SMA indicator's code from his article "Custom Indicators in MQL5 for Newbies" into code of more complicated and universal digital filter. This article is a logical sequel to the previous article. It also tells how to replace text in code and how to correct programming errors.