This part of ISO 8503 specifies the stylus instrument and describes the procedure for calibrating ISO surface profile comparators conforming to the requirements of ISO 8503-1. This part of ISO 8503 is also applicable to the determination of the surface profile, within the range Ry5 = 20 µm to Ry5 = 200 µm, of essentially planar blast-cleaned steel. The determination can be carried out on a representative section of the blast-cleaned surface or, if direct observation of the surface is not feasible, on a replica of the surface (see Annex C). NOTE Where appropriate, this procedure can be used to assess the roughness profile of other abrasive blast-cleaned substrates. An alternative procedure is described in ISO 8503-3.