1 Scope and field of application 1.1 Scope This part of ISO 4677 specifies a method for the determination of the relative humidity of atmospheres for conditioning and testing having temperatures within the range from 5 to 80 OC using a psychrometer ventilated by whirling. The property is determined with an uncertainty not exceeding + 3 % r.h. 1.2 Field of application The method is applicable to the determination of the relative humidity of the Standard atmospheres specified in ISO 554 and of most test atmospheres. lt is restricted to wet-bulb temperatures not lower than 1 OC, dry-bulb temperatures not higher than 80 OC, and pressures not differing from Standard atmospheric pressure by more than 30 %. The method should not be used if the atmosphere is heavily contaminated with gases, vapours or dust.