Despite appearances, the graph above has two lines. If you look really closely, you can see a second color peeking out here and there. And what two series are these that track each other so closely? One is the daily price of gold in London as of 10:30 a.m. The other is also the daily price of gold in London but as of 3 p.m. You’d expect these prices to be very close to each other, but let’s graph the percentage change between the price at 10:30 a.m. and 3 p.m. to see exactly how similar they are.
In fact, what we have here is a fairly volatile series.* Many of these price changes, which occur within 4.5 hours of each other, are in the range of 1% to 2%. Some even more. This rate of change is about the same as the rate of inflation in the U.S. Such changes in commodity prices aren’t uncommon, of course, even if trading occurs around the clock on world markets. The London market is open 8 a.m. to 5 p.m. (London time). These series are just snapshots during part of that time, but market activity continues in a similar fashion at other times and elsewhere.
How these graphs were created: Search for “gold” and the two series should be among the first choices. Select them and click on “Add to Graph.” For the second graph, start with the first one and use the “Edit Graph” panel to make adjustments: Open the tab for the second series and delete it (click on the trashcan). Then, in the tab for the first series, search for and add the second series and then apply formula (b-a)/a*100.
* NOTE: Because there are many daily observations for the period shown, the graph offers only a sample of them. To see the details, just shorten the sample time.
Suggested by Christian Zimmermann.