Calibration is non-critical. Getting within 5% is excellent. Getting
within 10% is usually acceptable
Assuming your spindle is a typical 3 phase 400 Hz induction motor,
it will not run 24,000 RPM at 400 Hz because all induction motors
will run slightly slower than synchronous speed. This is called the
slip angle and is essential to how an induction motor works.
If speed accuracy is important to you, I would suggest that you
use your control program to request some lower speed such as
20,000 and calibrate at that speed because you can get the VFD
to generate a higher frequency as needed there whereas the VFD
probably has a hard limit of 400 Hz at the top of the range and
cannot run over-frequency to compensate for the slip angle.
