Published article How to Write an Indicator on the Basis of Another Indicator 
In MQL5 you can write an indicator both from a scratch and on the basis of another already existing indicator, in-built in the client terminal or a custom one. And here you also have two ways - to improve an indicator by adding new calculations and graphical styles to it , or to use an indicator in-built in the client terminal or a custom one via the iCustom() or IndicatorCreate() functions.
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