A method, comprising: selecting a first modular component of a surgical instrument, the first modular component comprising a handle, a first attachment portion and an electric motor; selecting a second modular component of the surgical instrument, the second modular component comprising a shaft, a second attachment portion movable between a plurality of positions relative to said first attachment portion, wherein said plurality of positions comprises a disengaged position, an engaged position and a partially-engaged position, wherein said second modular component is secured relative to said first modular component when said second attachment portion is in said engaged position, and wherein said partially-engaged position is intermediate said disengaged position and said engaged position, and a drivable element in communication with said electric motor when said second modular component is secured relative to said first modular component, wherein said electric motor is configured to drive said drivable element during a firing stroke; positioning the first component relative to the second component; detecting the position of said second attachment portion relative to said first attachment portion including said partially engaged position via an engagement sensor, said engagement sensor comprising a plurality of sensors and/or electrical contacts staggered along said first attachment portion or said second attachment portion; and communicating the detected degree of engagement to an operator of the surgical instrument via a display and a microcontroller (604; 614) in signal communication with said engagement sensor and said display, wherein said microcontroller is configured to communicate the detected position of said second attachment portion to said display, wherein said microcontroller is in signal communication with said electric motor, and wherein said microcontroller prevents the firing stroke until said engagement sensor detects said engaged position. selecting a first modular component of a surgical instrument, the first modular component comprising a handle, a first attachment portion and an electric motor; selecting a second modular component of the surgical instrument, the second modular component comprising a shaft, a second attachment portion movable between a plurality of positions relative to said first attachment portion, wherein said plurality of positions comprises a disengaged position, an engaged position and a partially-engaged position, wherein said second modular component is secured relative to said first modular component when said second attachment portion is in said engaged position, and wherein said partially-engaged position is intermediate said disengaged position and said engaged position, and a drivable element in communication with said electric motor when said second modular component is secured relative to said first modular component, wherein said electric motor is configured to drive said drivable element during a firing stroke; positioning the first component relative to the second component; detecting the position of said second attachment portion relative to said first attachment portion including said partially engaged position via an engagement sensor, said engagement sensor comprising a plurality of sensors and/or electrical contacts staggered along said first attachment portion or said second attachment portion; and communicating the detected degree of engagement to an operator of the surgical instrument via a display and a microcontroller (604; 614) in signal communication with said engagement sensor and said display, wherein said microcontroller is configured to communicate the detected position of said second attachment portion to said display, wherein said microcontroller is in signal communication with said electric motor, and wherein said microcontroller prevents the firing stroke until said engagement sensor detects said engaged position.