Definition of Time Variables: how to ?

[#1]

Hey Experts,

I have the date variable and a key figure(K). I have two questions regard this:

1) how to define a variable, which is: Knew =Avg (Km-1+Km-2), where m could be based on monthly or daily level.

I want to see the delta between the current Key figure and the average of 2 or 3 past month?

2) What is the best way to visualize the deviaiton, i mean are there some extentions that are best suited for this?

Thank you very much in advance,

best,

Rustam