Arc length = arc radian x radius.
1 ppm means:
- 1 micrometer = 1 microradian x 1 meter, or
- 1 milimeter = 1 microradian x 1 kilometer.
From the viewpoint of Probability & Statistics for coordinate metrology, there must be uncertainties of HW and SW.
Once the HW accuracy is given, then the SW accuracy must be at least 3~5 times higher in order to not deteriorate the HW accuracy.
For example, if the measurement accuracy of HW is 3 mm, then the data processing accuracy of SW must be higher than 1 mm.
Total accuracy of (HW+SW) = sqrt( HW^2 + SW^2 ).
An example of calculation:
HW accuracy = 3 mm
SW accuracy = 1 mm
Total accuracy = sqrt( HW^2 + SW^2 ) = sqrt( 9 + 1) = about 3 mm = HW accuracy.
FindSurface's SW accuracy preserves the accuracy of HW.