the precision level will be affected by the spline order and montage density, a minimum of 20 iterations, but preferably 50 or more, is a good choice. Importantly, the time-consuming process for setting-up two montage-dependent transformation matrices (one for estimating the scalp distribution of surface potentials, and another one for the surface Laplacian), which will exponentially increase with montage density, must be done only once for a given montage. Once these two transformation matrices have been calculated, surface Laplacian estimates can be readily obtained for any sample point (i.e., any discrete EEG/ERP topography).11
