Do you want your record listed on the Billboard Hot 100?  You need a UPC bar code for each title.  Nielson Sound Scan uses upc codes to track record sales weekly.  When you call Nielson, they refer you to the GS-2 where you will pay a $750 membership fee before you purchase your first upc bar code.  Not necessary!

Here is a link to register your gotbarcodes.com upc codes with Nielson. http://titlereg.soundscan.com/soundscantitlereg/