Traditional measurement mode cannot measure the geometries without theoretical forms and parameters. Form-free measurement mode is presented to measure those geometries with high accuracy and efficiency. Critical techniques such as geometrical information extraction, form recognition and deviation assessment are analyzed. The automatic adaptive sampling strategy based on the local geometrical information is discussed. Six arithmetic operators for fast form recognition are derived. The probe radius compensation method is introduced. And deviation assessment based on Chebyshev approximation is analyzed. Form-free measuring mode is an evolutional innovation on precision measurement technologies and instruments.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.