As I type this post, I calculate the difference to be $689... since we had an ATH of $19,666 and we had a AYH from yesterday (about 17 hours ago) of $18,977.
is Bitstamp the official WallObserver exchange for prices?
on Bitfinex or Coinbase ATH was $19891.
Yes... we use bitstamp here for those kinds of general price discussions including ATH type issues, but if you have some point that you want to make about some other activities on other exchanges that includes price, then of course you can discuss those issues too.. and in that regard it would be good to mention which exchange(s) you are talking about..
Sometimes, of course, we will discuss exchange arbitrage type issues too, in order to figure out some of those dynamics, sometimes - which exchange arbitrage seems to be a bit less of an issue than it was in 2014, 2015, 2016, and even 2017 at least with the BIGGER ones.. but who knows about if those matters might rear their ugly heads again, , these days as compared to historically in which sometimes there would be 10% price differentiations between exchanges, and sometimes we discuss those kinds of difference of price matters too to the extent that it might be relevant to some point that is in discussion or that someone might want to bring up.... and of course, if you are making those kinds of comparisons, then mentioning which exchange(s) is/are at issue would help, too.
an explationary post by JayJuanGee gives all the information you need. Maybe a grain to much to compute.