An instantly playable stringed instrument having a body, neck and fret spaces is provided. A flicker component is detected using the luminance information of the image signal in the extracted flicker detection region. The drive gear is disposed at least partially within the housing and is rotatable about a drive gear axis which extends therethrough. In some embodiments, the authentication system may be operative to detect a visual or temporal pattern of inputs to authenticate a user. Calculations may be carried out after Booth encoding of operands.