Question about parameters in Roofit (paramOn)

Hi, everyone!

First time posting here, but I have been mildly using ROOT for a while. I only recently started using Roofit, and this problem has been bugging me for a long time, but I can’t seem to find the solution.

My case:
I simply fitted a binned histogram with a signal and a background component and I use the paramOn() to plot the parameters of the fit in the parameter box. I also use the Parameters() option to specify which I want to add.

My problems:

  1. Roofit gave me optimal values of Nsig and Nbkg, but I also want their sum to be added to the parameter bix. How can I do this so that the error is also shown ?

  2. What if I want to add a custom variable to the parameter box? I tried creating a RooAbsReal variable with the name and everything, but it wouldn’t show up in the box, even if I enabled the ShowConstants() option[/ul]
    Is the parameter box frequently used in this manner or any matter at all? Or is there a different, more intuitive way that you professionals use?