It is really lame that huge sites (Bloomberg, Yahoo Finance, CNBC, CNN, Marketwatch...) can't easily show what markets are closed. Instead they show changes (which imply changes today) that are often for the previous day. So half an hour before a market opens the display indicates it has returned whatever it returned yesterday. And if the market is closed that day, all day long the display acts as though it has the return it did that last day it was open.
Display on Bloomberg. But actually the Hong Kong market is closed today, bad Ux :-(
This feeble usability failure should have been fixed years ago. Yet as far as I can tell all the sites continue to fail to take sensible steps to make it clear what the real data for today is.
From Marketwatch, you have to look at the graph, see it isn't yet 2 PM in Hong Kong and then deduce the Hong Kong market isn't open today, bad Ux
On a much more minor point, eliminating tiny decimal places is better (as Marketwatch does but Bloomberg doesn't). 100% (99.999% rounded up :-) of users don't want to see the Nikkei is at 14,788.80 it is better to display 14,789. Similarly don't display fractions of a cent for stock quotes.
Related: Bad Visual Controls, Software - Customer Focus and Internet Travel Search - 6 years Later Goolge Acts To Let Me Block Sites I don't want to see (2011, then Google removed this useful feature so again lots of lousy sites clutter the results) - Understanding Technology and Programing is Vital - Gobbledygook (bad password usability)