I'm currently having difficulty calculating values for the deseasonalised sales column. How do you go about doing it for 2004Q1-2004Q2?
Btw in case you are wondering:
$$2004Q1$$
$$First MA = {\frac{20+12+9+7}{4}} = 12$$ $$Centered MA = {\frac{11.5+12}{2}} = 11.750$$ $${\frac{Sales}{CMA}} = {\frac{12}{11.750}} = 1.02$$
$$2004Q2$$
$$First MA = {\frac{12+9+7+25}{4}} = 13.75$$ $$Centered MA = {\frac{12+13.25}{2}} = 12.625$$ $${\frac{Sales}{CMA}} = {\frac{9}{12.625}} = 0.71$$
This is the pattern being followed throughout.