Foreign exchange traders care about trends. It is hard to work out a “fundamental” value for a currency, so trading patterns are often all they have to go on. If a long-term trend is breached, that can mean more to them than the latest economic data.

Look no further than the upheavals for the euro and the pound. Moving averages matter. If a currency regularly trades above or below its 200-day moving average (its rolling average over the last 200 days of trading), then a move through that average takes on great significance.