Power Calibration is controlled by the recorder. Before any write operation, all recorders must do a 15 step power test to determine the optimum power for writing to the CD; this is called "Optimum Power Calibration"(OPC). And during the write, it continues to do this test to get the best write throughout the whole CD; this is called "Running Optimum Power Calibration" (ROPC). This whole process is controlled by the recorder. There is an area on the inner part of the CD for the test and test data info to be stored.