Maybe add a legend to better indicate the seasonal and trading day frequencies
References (x13 and JD+ manuals)
Possibly include spec.ar()-function and adapt n.freq directly in this function. spec.ar() only allows for a parameter "n.freq=The number of points at which to plot" but not for a vector of frequencies at which to plot. Therefore the exact trading day frequencies can not be pointed out in our plots.
Possible further enhancements