docs: def V_actuation(self):
          '''
          Return the voltage drop across the device (i.e., the ``Z1`` load) for
          each feedback measurement.
  
          Consider the feedback circuit diagrams below for the feedback
          measurement circuits of the two the control board hardware versions.
  
          .. code-block:: none
  
                           # Hardware V1 #          # Hardware V2 #
  
                           V_1 @ frequency          V_1 @ frequency
                          ┬    ┯                        ┯
                          │  ┌─┴─┐                    ┌─┴─┐    ┌───┐
              V_actuation │  │Z_1│                    │Z_1│  ┌─┤Z_2├─┐
                          │  └─┬─┘                    └─┬─┘  │ └───┘ │
                          ┴    ├───O V_2                │    │  │\   ├───O V_2
                             ┌─┴─┐                      └────┴──│-\__│
                             │Z_2│                           ┌──│+/
                             └─┬─┘                           │  │/
                              ═╧═                            │
                               ¯                            ═╧═
                                                             ¯
  
          Note that in the case of **hardware version 1**, the input voltage
          ``V1`` is divided across ``Z1`` *and* the feedback measurement load
          ``Z2``. Therefore, the effective *actuation* voltage across the DMF
          device is less than ``V1``.  Specifically, the effective *actuation*
          voltage is ``V1 - V2``.
  
          In **hardware version 2**, since the positive terminal of the op-amp is
          attached to *(virtual)* ground, the negative op-amp terminal is also at
          ground potential.  It follows that the actuation voltage is equal to
          ``V1`` on **hardware version 2**.
          '''
          if self.calibration.hw_version.major == 1:
              return self.V_total() - np.array(self.V_fb)
          else:
              return self.V_total()