Estimates of the standard deviation of the correlator (upper panels) and (lower panels) along a single line of sight as a function of the source redshift z and of the length of the measured spectrum Δ z, for convergence maps reconstructed from Planck (left panels) and ACTPOL (right panels). As before, we set A = β = 1, effectively turning off the physics of IGM, to make apparent the physics of structure formation.