how can i match two files from same ACS year?

I downloaded a file from ACS, created a set of new variables, and then discovered I forgot to select one variable from the ACS data set on line. If I bring down that variable, what other variables do I need to match it with the same case? Thank you.

Within each ACS sample the variables SERIAL and PERNUM (which are automatically included in every extract) uniquely identify individuals. So if you create an extract with the variable you are missing you can merge the new extract onto your old extract using SERIAL and PERNUM.

You can also revise old extracts to include new variables by using the “revise” link on the row of the extract you want to update.

I hope this helps.