**4. Discussion**

When introducing displacement through the hinge, it is necessary to consider whether the introduced inclination will affect the measurement result. In our experiment, the inclination is very small and has little effect on the measurement of the out-of-plane displacement. The maximum displacement of the top end of the microchip is 9.6 μm, and the distance from the top end to the fixed axis is 11 mm. Thus, the inclination angle is about 0.00087◦. Through further calculation, the change in the vertical beam propagation direction does not exceed one pixel, so it will not affect the measurement results. In order to understand the displacement process easily, the angles drawn in Figures 8 and 12 are exaggerated and much larger than the actual angle.

If we want to measure the displacement in the case of a large inclination angle, we can no longer calculate the out-of-plane displacement only by Equation (7), but should consider the influence of the inclination angle and the in-plane displacement [35–37]. Yang, L.X. has summarized various out-of-plane displacement and in-plane displacement measurement methods and applicable conditions in detail [35].
