(a) True model varying between −100 and +100. (b) Unknowns are in dark blue and bi-points give dips, with small values included in the interval [−3.2, 3.2]. (c) Result of the inverse distance weighting, which preserves the data interval [−3.2, 3.2] with a yellow color everywhere. (d) Result of the multi-scale algorithm which preserves slopes and gives [−60, 60] overall range.