Which future contact to select while doing data backfill in Amibroker

Hi Guys,

I have question regarding Data filling to Amibroker. Which future contract should we go for to use the backfill the graph if i am using any data feed to Amibroker. Because as of now there are 3 contract March,April and May. I tried plotting the graph taking all 3 contract as NIFTY_F,NIFTY_F2,NIFTY_F3. All of them are having different graph values because the data table will have different values for same date and time for all 3 contract. So which futures contract should we consider when plotting the future graph. Attached are the graphs for all 3 contract.


March :-http://postimg.org/image/7uoaaztin/
April:-http://postimg.org/image/f0yjj3em5/
May:-http://postimg.org/image/5snswqvjj/

Your question is not clear can you specify in brief.