When probing an element, you have to make sure that
sufficient probing points are
taken and distributed uniformly and completely on the element. Otherwise, there is a risk that the element is measured incorrectly, incompletely or imprecisely!
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(Repetition) 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 7172 |
| 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 |
Rule of thumb: When measuring
datums: Measure, if possible, at least 4 times more probing points than mathematically necessary! |
