I've been struggling to understand how I should actually calculate the MA model, in particular - what mean do I take? In Wikipedia there's the formula:

[![enter image description here][1]][1]


in which as far as I understand the Mu is the population mean, which leads me to believe that it could be visualised this way:
[![enter image description here][2]][2]


and carrying out simple =linest function (forgive me for nonenglish excel version) leads us to MA(3):

[![enter image description here][3]][3]


My first question here - is my model correct? Can you see if I have misunderstood something?


My second question: While carrying out ARMA model, do I simply add the columns with lagged values like this?:

[![enter image description here][4]][4]


Or am I supposed to use the residuals of AR model as inputs to the MA part? This part is the most confusing to me, because I was learning how to do that by coding, which I feel didn't give me enough insight into the actual calculations.

PS: Please don't worry about the parameters I used, I'm aware of the necessity of testing the data before doing anything and I only used excel screenshots to express exactly where my problem is.

Have a nice day!


  [1]: https://i.sstatic.net/hDnxB.png
  [2]: https://i.sstatic.net/Nobeu.png
  [3]: https://i.sstatic.net/fQZ0u.png
  [4]: https://i.sstatic.net/O5Dla.png