A method for determining a depth ordering between two planes in a 3D workspace of an application is provided. The washer cassette includes an inlet opening and an exit opening with upper and lower entry rollers having a first predetermined durometer positioned adjacent to the inlet opening and upper and lower exit rollers having a second predetermined durometer positioned adjacent the exit opening. It is judged that the optical member is usable when the total area is not more than 10% of an effective diametric area or a partial diametric area of the optical element.