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.