Provided is an optical unit for a display panel device with a capacitive touch input function. The first frictional element is disengaged, engaged and disengaged when the transmission assumes the first, second and third speed stages respectively. A second lever is attached to the frame and can pivot with respect to the frame to engage a second filter. A new MAC value for each of the checker segments is then calculated. The present invention also provides a process for the preparation of tenofovir disoproxil or a salt thereof and its pharmaceutical composition using the tenofovir of the present invention.