Values of a,b,siga,sigb,chi2,q: Fit with x and y errors gives: -5.058982 2.022800 0.274606 0.020896 42.586632 0.038141 Setting x errors to zero gives: -5.538359 2.008888 0.110666 0.009359 277.534515 0.000000 ...to be compared with fit result: -5.538355 2.008888 0.104930 0.008537 277.534607 0.000000 Setting y errors to zero gives: -5.477011 2.043204 0.184831 0.012431 105.700813 0.000000 ...to be compared with fit result: -5.494889 2.044625 0.160466 0.012380 105.687607 0.000000