diff --git a/content/zettels/rotation_stage.md b/content/zettels/rotation_stage.md
index 60ad7f4..1f8f34b 100644
--- a/content/zettels/rotation_stage.md
+++ b/content/zettels/rotation_stage.md
@@ -67,6 +67,17 @@ Rotation at 60deg/s (10RPM).
 {{< figure src="/ox-hugo/rotation_stage_rt100bs_cas_error.png" caption="<span class=\"figure-number\">Figure 5: </span>Cumulative Amplitude Spectrum - RT100BS" >}}
 
 
+### Ultrasonic Piezo Motor Spindle (XRT-U-30) {#ultrasonic-piezo-motor-spindle--xrt-u-30}
+
+<https://xeryon.com/products/precision-rotation-stages/xrt-u-30/>
+
+Rotation at few degrees per second.
+
+```matlab
+length(axial_turns)/5 % Number of point per turn
+```
+
+
 ## Bibliography {#bibliography}
 
 <style>.csl-entry{text-indent: -1.5em; margin-left: 1.5em;}</style><div class="csl-bib-body">