The currency markets work 24 hours. Yahoo plots the intra day voltality but the graph that yahoo shows in that link does not chart all 24 hours and that is why you see a break which causes it to look like steps. The steps are going down because the currency seems to be on a downward trend.
I think he was really asking about the 5-day chart, which has a large stairstep upwards at 4:00 AM GMT on each day. The date range parameter apparently doesn't hotlink very well on Y!Finance.
