diff --git a/content/zettels/rotation_stage.md b/content/zettels/rotation_stage.md
index 6b9b4ba..7d3d51d 100644
--- a/content/zettels/rotation_stage.md
+++ b/content/zettels/rotation_stage.md
@@ -9,6 +9,12 @@ Tags
 : [Slip Rings]({{< relref "slip_rings.md" >}})
 
 
+## Spindle Metrology {#spindle-metrology}
+
+-   <https://ingeniqs.be/engipedia/spindle-metrology/>
+-   <https://ingeniqs.be/engipedia/error-separation-techniques/>
+
+
 ## Manufacturers {#manufacturers}
 
 | Manufacturers                                             | Country |
@@ -19,6 +25,65 @@ Tags
 | [PIC](https://www.airbearings.com/)                       | USA     |
 
 
+## Spindle Errors {#spindle-errors}
+
+
+### Air Bearing Spindle (RT150U) {#air-bearing-spindle--rt150u}
+
+<a id="figure--fig:rotation-stage-rt150u-xyz-errors"></a>
+
+{{< figure src="/ox-hugo/rotation_stage_rt150u_xyz_errors.png" caption="<span class=\"figure-number\">Figure 1: </span>RT150U - XYZ errors (eccentricity removed)" >}}
+
+```matlab
+%% Frequency Analysis
+Nfft = floor(10.0/Ts);
+win = hanning(Nfft);
+Noverlap = floor(Nfft/2);
+
+[pxx_ab_x, f_ab] = pwelch(x, win, Noverlap, Nfft, 1/Ts);
+[pxx_ab_y, ~   ] = pwelch(y, win, Noverlap, Nfft, 1/Ts);
+[pxx_ab_z, ~   ] = pwelch(z, win, Noverlap, Nfft, 1/Ts);
+```
+
+<a id="figure--fig:rotation-stage-rt150u-asd-errors"></a>
+
+{{< figure src="/ox-hugo/rotation_stage_rt150u_asd_errors.png" caption="<span class=\"figure-number\">Figure 2: </span>Amplitude Spectral Density of the Spindle errors" >}}
+
+<a id="figure--fig:rotation-stage-rt150u-cas-error"></a>
+
+{{< figure src="/ox-hugo/rotation_stage_rt150u_cas_error.png" caption="<span class=\"figure-number\">Figure 3: </span>Cumulative Amplitude Spectrum - RT150U" >}}
+
+
+### Mechanical Bearing Spindle (RT100BS) {#mechanical-bearing-spindle--rt100bs}
+
+```matlab
+%% 5 RPM - RT100BS from Lab Motion
+load('/home/thomas/mnt/data_mel/MEL/meas_equipment/spindle/RT100BS_roundness_5rev_5RPM.mat', 'data');
+
+Wz = 30; % 30 [deg/s] = 5 RPM
+x = 1e3*detrend(data.meet_data.raw, 0); % Radial Error [nm]
+
+Ts = 5*(360/Wz)/length(x);
+```
+
+```matlab
+%% Frequency Analysis
+Nfft = floor(10.0/Ts);
+win = hanning(Nfft);
+Noverlap = floor(Nfft/2);
+
+[pxx_mb_x, f_mb] = pwelch(x, win, Noverlap, Nfft, 1/Ts);
+```
+
+<a id="figure--fig:rotation-stage-rt100bs-asd-errors"></a>
+
+{{< figure src="/ox-hugo/rotation_stage_rt100bs_asd_errors.png" caption="<span class=\"figure-number\">Figure 4: </span>Amplitude Spectral Density of the Spindle errors" >}}
+
+<a id="figure--fig:rotation-stage-rt100bs-cas-error"></a>
+
+{{< figure src="/ox-hugo/rotation_stage_rt100bs_cas_error.png" caption="<span class=\"figure-number\">Figure 5: </span>Cumulative Amplitude Spectrum - RT100BS" >}}
+
+
 ## Bibliography {#bibliography}
 
 <style>.csl-entry{text-indent: -1.5em; margin-left: 1.5em;}</style><div class="csl-bib-body">
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