Dear all: John C. Frain, thank you. So if I choose the options Model/Time series/ARIMA/Using X-12-ARIMA to run the X-12-ARIMA model. The explanatory variables such as as number of working days, day of week effects, length of month etc are all automatically already included, they are just not shown in the output of gretl, right? Or I have to choose these variables by myself? Are all the explanatory variables the same as RegARIMA in X-12-ARIMA – Reference Manual, Version 0.3. (U.S. Census Bureau) ? Thanks a lot