NBBO? Whos makes up the NBBO?

NBBO- National Best Bid or Offer. Who makes up the NBBO, I assume Nasdaq and NYSE quotes make part of it up. But what if NYSE is quoting an Offer of $50.40 and TRAC ECN is quoting an Offer of $50.38, then the NBBO would be $50.40 because TRAC isn't used to determine NBBO? So who's quotes are use to determine the NBBO? Now BATS is it's own Exchange, so do their quotes determine NBBO now? What about DirectEdge, they quote through the NSX Exchange, so does that mean their quotes are exchange quotes and determine the NBBO? Can some one please give me some clarification on this, or better yet Links to websites that are descriptive about what it takes for a quote to determine the NBBO? I already tried the SEC and other searches but didn't find the answer I am looking for and don't want to spend 12 hours going through the SEC webpage.

Thanks

 

Bump, to the front of the line, it's almost lunchtime, more viewers.

 

just look at level 1 and there is your answer:eek:

 

i ask my broker same question few years ago,when my trade got busted,because it's "outside of NBBO". how to hell it's outside of NBBO, if i bought @ the bid and i'm only a bidder at that time and price?