Hello

thanks for your answer, I attach a simple example below. The results of the fit do not change,

no matter how large or small are the x-errors.

It seems the y-errors instead are taken into account.

{

c1 = new TCanvas(“c1”,"",200,10,700,500);

Int_t n = 3;

Double_t x[n] = { 0.35, 0.5, 1.61};

Double_t y[n] = {7.4,9,9.6};

Double_t xerr_low=2.05.;

Double_t xerr_high=2.05;

Double_t exl[n] = {.05,.051,err_low};

Double_t exh[n] = {.05,.05,err_high};

Double_t yerr_low=0.05.;

Double_t yerr_high=0.05;

Double_t eyl[n] = {.5,.4,yerr_low};

Double_t eyh[n] = {.3,.2,yerr_high};

gr = new TGraphAsymmErrors(n,x,y,exl,exh,eyl,eyh);

gr->SetMarkerColor(4);

gr->SetMarkerStyle(21);

gr->Draw(“AP”);

gr->Fit(“pol1”,“F”);

return c1;

}