A method, including acquiring initial signals from selected positions in a heart, computing respective initial local values of a signal propagation metric at the selected positions, and interpolating the initial local values between the selected positions to compute initial interpolated values of the signal propagation metric at intermediate positions, between the selected positions. The method further includes acquiring subsequent signals from the positions, computing respective subsequent local values of the signal propagation metric at the selected positions, and spatially interpolating the subsequent local values of the signal propagation metric between the selected positions to compute subsequent interpolated values of the signal propagation metric at the intermediate positions. A map of the signal propagation metric is displayed, and when the subsequent interpolated values exceed a bound defined with respect to the initial interpolated values, an indication is provided on the map that the bound has been exceeded.