A method of characterising particles in a sample , comprising: illuminating the sample in a sample cell with a light beam , so as to produce scattered light by the interaction of the light beam with the sample ; obtaining a time series of measurements of the scattered light from at least one detector ; determining , from the time series of measurements, which measurements were taken at times when a large particle was contributing to the scattered light a large particle being a particle with a diameter larger than a predetermined threshold size or wherein a dynamic criteria, determined from the time series of measurements, is used to categorise particles as large, wherein determining which measurements were taken at times when a large particle was contributing to the scattered light comprises: dividing the time series up into a plurality of shorter sub-runs, and then determining which of the sub-runs comprise measurements with a scattering contribution from a large particle; determining a particle size distribution from the time series of measurements, including correcting for light scattered by the large particle, wherein correcting for light scattered by the large particle comprises excluding sub-runs taken at times when the large particle was contributing to the scattered light ; and the method being characterised in that it comprises performing an initial number of sub-runs, with further sub-runs being recorded and added to the preceding measurements if they are not excluded until an average obtained from the combined measurements has met a convergence criteria based on the amount the average obtained from the combined measurements changes over a number of succeeding measurements. illuminating the sample in a sample cell with a light beam , so as to produce scattered light by the interaction of the light beam with the sample ; obtaining a time series of measurements of the scattered light from at least one detector ; determining , from the time series of measurements, which measurements were taken at times when a large particle was contributing to the scattered light a large particle being a particle with a diameter larger than a predetermined threshold size or wherein a dynamic criteria, determined from the time series of measurements, is used to categorise particles as large, wherein determining which measurements were taken at times when a large particle was contributing to the scattered light comprises: dividing the time series up into a plurality of shorter sub-runs, and then determining which of the sub-runs comprise measurements with a scattering contribution from a large particle; determining a particle size distribution from the time series of measurements, including correcting for light scattered by the large particle, wherein correcting for light scattered by the large particle comprises excluding sub-runs taken at times when the large particle was contributing to the scattered light ; and the method being characterised in that it comprises performing an initial number of sub-runs, with further sub-runs being recorded and added to the preceding measurements if they are not excluded until an average obtained from the combined measurements has met a convergence criteria based on the amount the average obtained from the combined measurements changes over a number of succeeding measurements. <EOS>