What does coded to double and old and new barcode mean??

Those of us who have been doing this so long don't even think about throwing around terms like old and new barcode coded to double will double but says don't.  How do we know???  How can you tell??  Well I am hoping this new section of my blog can and will answer all those questions feel free to use the contact form below to ask me coupon questions I want everyone to be able to save a ton of $$$  that is my goal so ask!!!  Your question may be featured on the next segment of this blog page!!!