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**.

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()