A bi-directional RAM is coupled between a first control device for data transfer using a first clock frequency and a second control device for data transfer using a second clock frequency having no multiple relation with the first clock frequency. A computing device is configured to have a desired force setting. The optical properties of the light within the optically transparent region are measured using an optical sensor positioned within the optically transparent region so that the light generated by the light source devices can be selectively adjusted to control the illumination.