Hello - Please excuse for delay in responding. 1. What is the logic with BACK option?   Please check out: https://communities.sas.com/t5/SAS-Forecasting-and-Econometrics/out-of-sample-range-and-holdout-sample/m-p/225886/highlight/true#M1387 which should give you some hints.   2. Currently ESM does not allow you to incorporate inputs like logprice. My suggestion would be to look at UCM instead. Check out: http://support.sas.com/documentation/cdl/en/etsug/68148/HTML/default/viewer.htm#etsug_ucm_examples04.htm to get started.   3. You will find some additional books here: https://www.sas.com/store/books/products-solutions/sas-ets/cBooks-cbooks_productsandsolutions-cbooks_productsandsolutions_ETS-p1.html I would also recommend to check out: https://www.otexts.org/fpp   Thanks, Udo ... View more