The price movements of both codes is then calculated into a percentage value.  The percentage value for the first code is then subtracted from the second code leaving the percentage difference between the two.  This is the value plotted on the chart.  The higher the value, the greater the difference in price between the first code and the second code.  The lower the value, the price difference between the two codes is smaller.  When the value is a negative, the price of the second code has overtaken the price of the first.

In the above example BHP and RIO are being compared from the 1st of October 2008 until now.

Creating a Percentage Difference Spread Chart

To open a Percentage Difference Spread, click on the New menu, go to the Spreads section and select the Percent Difference Spread option.

The Security Selector window will display:

Type in the first code you wish to use and press Enter on your keyboard.  The code will be added to the Compare Codes section on the bottom left corner of the screen.

Type in the second code you wish to compare to the first and press Enter on your keyboard.  The code will be added to the Compare Codes section on the bottom left corner of the screen.

With both codes entered, locate the Create Spread Chart button along the top of the Security Selection window and left click it once.

The Percentage Difference Spread will display.

Setting the Starting Date

By default the Percentage Difference Spread will display the entire price history for both codes.  You can adjust this however to any date by left clicking on the chart, going to the Control Panel on the left hand side of the screen and adjusting the Data to Load option listed under the Properties section to Selected.

The Date to Load Data From field will display below the Data to Load option.  Select the date you want the chart to begin plotting from and the data will adjust automatically.