NGX, TopCat, assumed flex temp etc

[Fi5kuS 57]

Hi.

 

So I have been getting PFPX and Topcat to match perfectly now in terms of ZFW. It does not 100% match the value I obtain when I load the numbers in the NGX FMC, but it is only a matter of 0.2-0.4 difference.

 

However, I want to get more serious using the takeoff-performance data from Topcat. Normally, I just enter flaps setting, thrust config etc and calculate performance data based on a certain runway. This gives you a set of assumed flex temperatures, usually de-rated. My understanding of these values are really poor and I don't know what values that are relevant and to be used in the takeoff-performance page in the FMC.

 

Can someone elaborate on this topic, and moreover, explain how you obtain similar (or preferably equal) values in Topcat and the NGX FMC.