his part of ISO 8503 specifes the optical microscope and describes the procedure for calibrating ISO surface profle comparators conforming to the requirements of ISO 8503-1.This part of ISO 8503 is also applicable to the determination of the surface profle, within the range hy= 20 µm to 200 µm, of essentially planar blast-cleaned steel. The determination can be carried out on a representative section of the blast-cleaned substrate or, if direct observation of the surface is not feasible, on a replica of the surface (see Annex E).NOTE Where appropriate, this procedure can be used for assessing the roughness profle of other abrasive blast-cleaned substrates.An alternative procedure is described in ISO 8503-4.