A measurement and processing technique enabling x-ray analysis systems to handle dynamically changing samples and other conditions resulting in both significant and insignificant measurement changes. A stream of input values related to measured compositional information of the sample is received, and a stream of output compositional values is produced. The current output value y[n] is set as a function of the received input value x[n] if the received input value x[n] differs from x[n-1] by more than an intensity-dependent deviation limit; and alternatively the current output y[n] is set as a function of the previous output y[n-1] and the received input value x[n] if the received input value x[n] differs from x[n-1] by less than the intensity-dependent deviation limit. The intensity-dependent deviation limit is maintained as a function of the intensity of the measured compositional information. Types of dynamically changing samples to which the technique is applicable include fluid streams and sheet production, monitored by, e.g., XRF and XRD systems.