a method of interfacing a person with a computer , the method comprising : providing the person with a device having : a shaft having an axis ; a tsuba connected to the shaft and having a first side that extends away from the axis and faces the shaft ; and a handgrip on a second side of the tsuba opposite the first side ; acquiring an image of the device ; determining an orientation of the device responsive to the image ; and generating an action by the computer responsive to the orientation .