Fellow Power BI Users 
Thank you for this Useful Workshop I have some questions in this regard:
Q1 Can you give me the steps on how to create the Input box with (slicer) for accepting the Chrun Time Frame?
For the Churn Time Frame = GENERATESERIES(0, 450, 15) , what do the 3 numbers series between () mean?
Q2 I have some difference in the Numbers of (Lost Customers) with the same filters between Your Video and the downloaded report on my machine?
Q3 Is the flag (1) Indicating the customer who is lost?
To create that input box is just using the ‘what if’ functionality.
See here

I’m not sure about the differences as there is a lot going on and you having included then in the images from what I can see.
I also wouldn’t get too caught up on these, just really focus on the technique and try understand what’s going on behind the scenes with the calculation engine to get the results.

Yes in this particular case the formula is showing minus one for a lost customer
Sam , For the data I note that there is actual data in Sales Table till (2019) , for The Data On 2020 can we consider it as a forecasting for (lost customer) & (Customer revenue lost) or automatic calaculation?
Some of the demo data I create projects forward to future dates. I do this so that the demos work for sometime into the future.
Totally up to you how you use it.
Sam Back again to the Table Below:
The First Row (Jul 2016) The New Purchased Customers are 290 and Actually no lost customers cuz (90) day from starting the business still running and the Total Customers actually will be 290 (I understand this No Problem).
The second raw (Aug 2016) Additional 192 new customers purchased in this month come to the Total Number of customers should be (192 + 290 (from previous month)) = 482 But the total customers written (295) on this row can you explain how this number come (295) ?
My Interpretation is : The total no of customers purchased in Jul 2016 Are 290, On August 2016 new purchases done by 5 customers whom already purchase in July and become 295 as total customers purchased (Previous Month + Current Month) among those 295 customers 192 (In August) of them are new , so the Net of steady customers will be 295192= 103 (Correct me If I’m wrong).
Thank you
No that’s not the right interpretation of this particular formula and the way it’s been setup
Total customers is just counting the distinct customer in every month. It’s not looking back at all and calculating a unique cumulative total.
Total Customers = DISTINCTCOUNT( Sales[Customer ID] )
Then steady customers is calculating total minus new customers. That’s it. It’s much simpler than your thinking.
So in summary steady customer is just evaluating how many customer purchased in any particular month but aren’t consider new, so they HAVE purchase at some point in the last 90 days.
Ok , Now I Understand It’s very simple thanks for the clarifications.