Nextrend has a free delayed service (try this before you pay for anything), a $14.95 real-time, $49.95 real-time, $79.95 real-time.
For real-time the $14.95 should work just fine. All the above services allow you to do spreads.
Below (in the attached file) is a 5 minute line chart of the SPY/QQQ spread (to show you an example). You can go anywhere from 1 minute up to monthly bars.
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To chart a spread in Nextrend, create a formula and add the formula to the chart.
How to create the spread formula:
Select the "Formula" icon on the left
Select "Add"
Type in a Formula name example"Spread"
We are going to create the formula so that you can use different symbols on
the same formula or if you want type in the specific symbol
This is the expression: ?1.LAST - ?2.LAST
Select "Check" to make sure there are no type-o's
Select "OK"
Select "Close"
Now add the Formula to a chart
Right-click over the background of the chart
Select "add elements"
Select "Formula"
Select the dropdown for Formula and select the spread formula
Replace the ?1, ?2 with the desire symbols for the spread (SPY, QQQ)
Select "Finish"
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http://www.nextrend.com/analysis/content/SvcLvls.asp