We have seen in the previous chapter that surface interactions cannot be accurately characterized without knowing the separation distance between the interacting surfaces. Likewise, the mechanics of contact between two surfaces can only be properly described if the geometry as well as the extension of the contact area is unambiguously known. However, absolute distances and contact areas are not directly measurable by any of the available scanning probe microscopy (SPM) techniques. Instead, they have been the result of assumptions that may lack applicability in some cases. Help is needed, and it readily comes in the shape of an additional optical technique: reflection interference contrast microscopy (RICM). This technique can infer the absolute distance between two nearby surfaces or the geometrical profile of two surfaces in contact from interference patterns.