diff --git a/content/zettels/voice_coil_actuators.md b/content/zettels/voice_coil_actuators.md
index f4699ba..0080fa8 100644
--- a/content/zettels/voice_coil_actuators.md
+++ b/content/zettels/voice_coil_actuators.md
@@ -56,13 +56,17 @@ As the force is proportional to the current, a [Transconductance Amplifiers]({{<
 
 ## Voice Coil for Vertical payload {#voice-coil-for-vertical-payload}
 
-Let's consider a spring-mass system with a force actuator.
+Let's consider a spring-mass system with a force actuator (Figure [1](#figure--fig:voice-coil-vertical-mass-spring)).
 Parameters are:
 
 -   `m`: the mass payload in [kg]
 -   `k`: the spring constant in [N/m]
 -   `Fmax`: the maximum force applied by the voice coil in [N]
 
+<a id="figure--fig:voice-coil-vertical-mass-spring"></a>
+
+{{< figure src="/ox-hugo/voice_coil_vertical_mass_spring.png" caption="<span class=\"figure-number\">Figure 1: </span>Mass Spring System" >}}
+
 `Dg`: deflection due to gravity in [m]
 `Df`: maximum stroke using the voice coil in [m]
 `f0`: the resonance frequency of spring-mass system in [Hz]
@@ -101,7 +105,7 @@ Fmax = k * Df; % [N]
 
 <a id="figure--fig:voice-coil-force-fct-f0"></a>
 
-{{< figure src="/ox-hugo/voice_coil_force_fct_f0.png" caption="<span class=\"figure-number\">Figure 1: </span>Required Voice Coil Force as a function of the paylaod resonance and corresponding deflection due to gravity (mass is 5kg, stroke is 5mm)" >}}
+{{< figure src="/ox-hugo/voice_coil_force_fct_f0.png" caption="<span class=\"figure-number\">Figure 2: </span>Required Voice Coil Force as a function of the paylaod resonance and corresponding deflection due to gravity (mass is 5kg, stroke is 5mm)" >}}
 
 
 ### Determine the payload resonance as a function of the wanted stroke {#determine-the-payload-resonance-as-a-function-of-the-wanted-stroke}
@@ -125,11 +129,11 @@ Dg = m * g ./ k; % [m]
 
 <a id="figure--fig:voice-coil-resonance-fct-stroke"></a>
 
-{{< figure src="/ox-hugo/voice_coil_resonance_fct_stroke.png" caption="<span class=\"figure-number\">Figure 2: </span>Resonance frequency and deflection due to gravity as a function of the wanted stroke (Max voice coil force is 50N and payload mass is 5kg)" >}}
+{{< figure src="/ox-hugo/voice_coil_resonance_fct_stroke.png" caption="<span class=\"figure-number\">Figure 3: </span>Resonance frequency and deflection due to gravity as a function of the wanted stroke (Max voice coil force is 50N and payload mass is 5kg)" >}}
 
 <a id="figure--fig:voice-coil-stiffness-fct-stroke"></a>
 
-{{< figure src="/ox-hugo/voice_coil_stiffness_fct_stroke.png" caption="<span class=\"figure-number\">Figure 3: </span>Resonance frequency and deflection due to gravity as a function of the wanted stroke (Max voice coil force is 50N and payload mass is 5kg)" >}}
+{{< figure src="/ox-hugo/voice_coil_stiffness_fct_stroke.png" caption="<span class=\"figure-number\">Figure 4: </span>Resonance frequency and deflection due to gravity as a function of the wanted stroke (Max voice coil force is 50N and payload mass is 5kg)" >}}
 
 
 ## Bibliography {#bibliography}
diff --git a/static/ox-hugo/voice_coil_vertical_mass_spring.png b/static/ox-hugo/voice_coil_vertical_mass_spring.png
new file mode 100644
index 0000000..4138b34
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