I had sales data of bikes from a course and I don’t think I would be allowed to share the code, but the help I need is not really coding, but understanding the results/graph. This is more conceptual.

How can the Revenue for certain sales data points shift if in reality the sale was at around $2,000,000 per say and now it is around $1,000,000 after adjusting for seasonality? Basically, all the data points are squeezed toward the x-axis, but in reality those sales must be greater so how can I even quantitatively interpret the results after adjusting for seasonality? A follow up question if you’d like is why even after adjusting for seasonality it looks like it is seasonal? I think from university they said take the second difference then. Did I do it right? (Ultimately, I am trying to conceptualize comparing original data set but take out the seasonality effect so I can compare with same products, but with a promotion. AM I going about this the right way? Do I even need to take out the seasonal factor?)

First Difference

Second Difference