Simple code to get the EMA of a custom indicator

I have this indicator which I am using with an embebbed 21 EMA on the MT4 chart.

I want to obtain the EMA value in code for a specific bar.

The job is simply to write the code (use a simple MQL “script”) using a simple “iCustom” call, apply the MA (EMA, not SMA!) and get the value of the EMA returned to a variable. The value must match the EMA value shown on the chart. I will want a way of checking the returned value with the value showing on the chart. 

I believe this won't take more than a few hours for an experienced math-oriented MQL4 coder.

Thank you.