It is an object of the present invention to provide a polishing pad that is resistant to scratching and also has excellent flattening performance. The first resistor network includes a set of transistors and receives a constant current from a constant current source. A pressure testing gas delivery system is interconnected with the test probes and selectively communicates pressurized gas to the testing tubes at a blow-down pressure or selected test pressure determined by restricted orifices. The inner and outer claddings of the multiclad output fiber have respective refractive indexes which are selected so that the refractive index of the outer cladding is higher than that one of the inner cladding.