Basics of Coordinate Metrology
Unit 6:  Basics of Metrology - Probing points

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The measuring strategy is determined by the expected form deviations and the required measuring uncertainty values. The measuring strategy includes the number and distribution of probing points per geometric element.

Please note the following: The minimum number of probing points has already been established mathematically by the geometry (see Unit 4: Geometry). However, the selected number of probing points should be many times higher than that.
  

Geometric element mathematical minimum number
of probing points

recommended number of probing points according to British standard BS 7122
Line 2 5
Plane 3 9
Circle 3 7
Sphere 4 9
Cylinder 5 4 parallel circles à 3 probing points for straightness check
  
Cone 6 as for cylinder

Tip: Unless a different approach makes sense, the probing points should always be distributed on the geometric element to be detected as uniformly as possible.

The measured points of the part geometry are called extracted geometry.
Number and distribution
of the measured points







Probing points