A surgical stapling instrument, comprising: a displacement member configured to translate within the surgical instrument over a plurality of predefined zones; an energy source; a motor coupled to the displacement member to translate the displacement member; a control circuit coupled to the energy source and the motor; a position sensor, the position sensor configured to monitor the position of the displacement member; wherein the control circuit is configured to: initiate firing the displacement member at a predetermined electrical load on the energy source, wherein the predetermined electrical load is applied to the motor to actuate the displacement member; characterised in that the position sensor is coupled to the control circuit and the control circuit is configured to: monitor the position of the displacement member via the position sensor; continually sample a voltage of the energy source during a first interval of travel of the displacement member as determined by the position sensor; compare the sampled voltage to a threshold voltage; and continue firing the displacement member at the first velocity when the sampled voltage is greater than or equal to the threshold voltage; and adjust the first velocity when the sampled voltage is less than the threshold voltage. a displacement member configured to translate within the surgical instrument over a plurality of predefined zones; an energy source; a motor coupled to the displacement member to translate the displacement member; a control circuit coupled to the energy source and the motor; a position sensor, the position sensor configured to monitor the position of the displacement member; wherein the control circuit is configured to: initiate firing the displacement member at a predetermined electrical load on the energy source, wherein the predetermined electrical load is applied to the motor to actuate the displacement member; characterised in that the position sensor is coupled to the control circuit and the control circuit is configured to: monitor the position of the displacement member via the position sensor; continually sample a voltage of the energy source during a first interval of travel of the displacement member as determined by the position sensor; compare the sampled voltage to a threshold voltage; and continue firing the displacement member at the first velocity when the sampled voltage is greater than or equal to the threshold voltage; and adjust the first velocity when the sampled voltage is less than the threshold voltage. initiate firing the displacement member at a predetermined electrical load on the energy source, wherein the predetermined electrical load is applied to the motor to actuate the displacement member; characterised in that the position sensor is coupled to the control circuit and the control circuit is configured to: monitor the position of the displacement member via the position sensor; continually sample a voltage of the energy source during a first interval of travel of the displacement member as determined by the position sensor; compare the sampled voltage to a threshold voltage; and continue firing the displacement member at the first velocity when the sampled voltage is greater than or equal to the threshold voltage; and adjust the first velocity when the sampled voltage is less than the threshold voltage. monitor the position of the displacement member via the position sensor; continually sample a voltage of the energy source during a first interval of travel of the displacement member as determined by the position sensor; compare the sampled voltage to a threshold voltage; and continue firing the displacement member at the first velocity when the sampled voltage is greater than or equal to the threshold voltage; and adjust the first velocity when the sampled voltage is less than the threshold voltage. continue firing the displacement member at the first velocity when the sampled voltage is greater than or equal to the threshold voltage; and adjust the first velocity when the sampled voltage is less than the threshold voltage.