corn contracts shown identical but they're not

[Tasuki]

I must have some setting wrong somewhere, because NT shows both the Jul and Dec contracts of ZC, corn, to be identical---but they're not!
In the second pic attached, I show the OHLC for three corn contracts, Jul, Sep and Dec, and as you can clearly see, all 3 are different--these values come from commoditycharts.com (but no matter where they came from, commodity contracts with different expirations are pretty much never identical).
WHY on earth is Ninjatrader showing two different contracts as if they were the same contract?
Must be something wrong somewhere. Please advise.
Thanks,
Tasuki

[NinjaTrader_Jason]

Hello Tasuki,

Can you please go to Control Center-->Tools-->Options-->Data-tab and set 'Merge policy' to 'DoNotMerge'. Click OK and reload historical data in the chart. Check if data is loaded as expected.

[Tasuki]

Thanks, Jason, that worked, but it shows that I need more of an education on the math and mechanics of merging. Does NT have an article on this subject somewhere?
Tasuki

[NinjaTrader_Jason]

Please see the link below under 'Understanding merge policies' for information regarding the merging process.

http://ninjatrader.com/support/helpGuides/nt7/historical_data.htm

If you create a ZC 12-16 chart today (with merging enabled), it loads all historical data from the 07-16 expiry month and realtime data is received from the 12-16 expiry month. This is why they show the same initially. If you disable merging, it will only load 12-16 data in the ZC 12-16 chart.