A color wheel is disclosed that has at least one segment that occupies, for a given radius, a percentage of the circumference of the wheel at that radius, which percentage varies continuously or in multiple steps from a radially inward point to a radially outer point on the wheel. The invention allows the efficient analysis of expression levels across each of these coding sequences. The velocities and positions of the first and second articles are measured during the transporting process. The elastic engaging member includes an engaging surface, and is non-rotatably sleeved on the shaft.