Key Takeaways:
Roundness testers must rotate the part or stylus with near-zero runout. Hydrostatic spindles supply the sub-micron, drift-free rotation that true roundness measurement requires.
圆度 Needs Perfect 轴
A 圆度 measuring instrument compares part's profile against ideal circle. If rotating 轴 itself has 径向跳动, 该 error为measured as if it were part's—corrupting 结果. reference 回转 must be near perfect.

静压 as Reference
A 静压主轴提供径向跳动 不超过 0.1 μm采用no low-speed 爬行与no thermal drift. 该 makes it ideal reference 轴用于圆度 testers, 其中 instrument's own error budget must be tiny fraction的 tolerance being checked.
Practical Benefit
Because film does not wear, tester's reference 精度 stays constant用于years, avoiding creeping measurement error 该 wears mechanical 主轴 introduce.