Values of a,b,siga,sigb,chi2,q: Fit with x and y errors gives: -5.058981 2.022800 0.274584 0.020894 42.586620 0.038141 Setting x errors to zero gives: -5.538360 2.008888 0.110666 0.009359 277.534546 0.000000 ...to be compared with fit result: -5.538355 2.008888 0.104930 0.008537 277.534485 0.000000 Setting y errors to zero gives: -5.477015 2.043205 0.184814 0.012429 105.700706 0.000000 ...to be compared with fit result: -5.494893 2.044625 0.160466 0.012380 105.687553 0.000000