This part of ISO 13317 specifies the method for the determination of particle size distribution by the mass of particles settling under gravity in liquid. This method is based on a direct mass measurement and gives the mass distribution of equivalent spherical particle diameter. Typically, the gravitational liquid sedimentation method applies to samples in the 1 μm to 100 μm size range and where the sedimentation condition for particle Reynolds number less than 0,25 is satisfied.