A chemical mechanical polishing apparatus and method can use an eddy current monitoring system and an optical monitoring system. One control logic circuit suffices for several memory circuits, reducing cost. The relative positions between positioning elements of the module are fixed so that the transport system does not need to be recalibrated when the processing chamber is removed and replaced with another processing chamber. The lid may further include a second closure on the panel, where the second closure may be configured to cover the second dispensing opening.