ISO 48:2007 specifies four methods for the determination of the hardness of vulcanized or thermoplastic rubbers on flat surfaces (standard hardness methods) and four methods for the determination of the apparent hardness of curved surfaces (apparent-hardness methods). The hardness is expressed in international rubber hardness degrees (IRHD). The methods cover the hardness range from 10 IRHD to 100 IRHD. The methods differ primarily in the diameter of the indenting ball and the magnitude of the indenting force, these being chosen to suit the particular application. The determination of hardness by a pocket hardness meter is described in ISO 7619‑2. Determination of the apparent hardness of rubber-covered rollers is dealt with separately in the various parts of ISO 7267.