Question about chi^2 test


I have a data_histo and the MC_histo (unweighted) and I want to calculate the chi^2/n.d.o.f .

Now in general, the MC_histo needs to be scaled first to the data, but I want to use the uncertainly of the “full” MC (unweighted ) histo in the calculation of the chi^2 since this is small while the uncertainty of the scaled MC is larger.

How is this possible ?