Fig 2.

a) Coordinate frames: NanoTracker coordinate frame xy, tip of the fiber frame x'y'. Note that the frame x'y' is moving with the fiber. The original position (before trap was displacement) of the frame x'y' is marked x'₀y'₀. Rotation angle between xy and x'₀y'₀ is α, between x'₀y'₀ and x'y' is Δα. b) The fiber deflection H is a projection of the bead displacement vector $\overrightarrow{d}$ on the trap displacement vector $\overrightarrow{r}$. Vectors $\overrightarrow{d}$ and $\overrightarrow{r}$ are not equal due to finite trap stiffness and a force, acting on the bead.