Impact of the choice of pair line-of-sight definition on the estimated monopole (upper panel) and quadrupole (lower panel) correlation functions in FGM mock. The curves show the absolute value of the difference between using mid-point and end-point definitions in the estimator for the monopole and quadrupole correlation functions. The different colours show this quantity for the redshift intervals: 0.9 < z < 1.1, 1.1 < z < 1.3, 1.3 < z < 1.5, 1.5 < z < 1.8. The dotted (dashed) line shows the expected 1σ (2σ) statistical error in the completed Euclid Wide Survey in the interval 1.1 < z < 1.3.