# X12 for seasonality adjustment - SAS

I found this code online and I wanted to dissect it before programming something similar in SAS.

The problem is idenitfy seasonality in a time series. I want to understand the code line by line:

proc x12 data=sales date=date season=12;
var unempl_rate *already log differenced;
transform function=none;
regression predefined=td;
automdl maxorder=(1,1)
print=unitroottest unitroottestmdl autochoicemdl best5model;
estimate;
x11;
output out=out(obs=23) a1 d11 d18;
run;
proc print data=out(obs=23);
title 'Output Variables Related to Trading Day Regression';
run;


By line:

1. the first line just defined use the x12 procedure with data set called "sales" - monthly data, indexed by variable "date" and expect a seasonality in the data every 12 months.
2. this line tells which variable to analyze.
3. no transformation was necessary since a transformation was already done.
4. this line confuses me a little, is "regression predifined=td" applied for adjustment/outliers/events?

5-7. do these lines mean to estimate the best ARIMA (linear) models on the residual? 8-onwards. For outputing results