Measurement methods and processing device

The invention relates to measurement methods, in which emits a measuring beam (24) taking place during a machining by means of a beam (16) machining a workpiece (17) is passed to a processing location (32) and then analyzed by interferometry. The measuring beam (24) is passed here through a focusing optics (18), through which also the machining beam (16) to the processing location (32) for machining the workpiece (17) is passed.