Evolution of gap eccentricity (top) and semi-major axis (bottom) for a binary with e_bin = 0.30. Shown are different measurements for the disc eccentricity. The red lines (e_gap and a_gap) show the eccentricity and semi-major axis of the geometrically fitted ellipses, see Fig. 8. The blue lines (e_max and a_max) show the eccentricity and semi-major axis of the cell with the maximum surface density. The green curve shows the averaged eccentricity of the inner disc. Since the gap size varies with time we use R₂ = R_Σmax in Eq. (18)to calculate the inner disc eccentricity.