id be very careful when using ohlc spread charts. most folk use close only.
you MUST know how the chart calculates the ohlc of the spread.
some will just use the difference between the outrights, but for example, the 2 highs of each leg could have occurred at different times of the day, giving a high, when in fact, the spread may never have traded there at all. typically, these will be found on 'expression' charts, where you calculate the spread by subtracting the short contract from the long.
eg gedu6-gedu5
some packages will chart the actual spread, but ONLY when the spread is traded as an exchange recognized strategy - such as eurodollar cals or crush spreads, where spreads trade as a product (almost) and have their own prints. then a reliable ohlc can be obtained.
i have no idea which cqg or barchart.com calculate. all spread traders i know of do so on an end of day basis, so only use the close (line chart)