These AEM LSU 4.2 sensors have a laser-etched, calibrated resistor in the sensor's connector body. This resistor is specifically created for the exact sensor that it is attached to. Modifying this will invalidate the sensor's output. The wideband sensor is laboratory-calibrated at the Bosch factory, accurate to 0.1 AFR and never requires free-air calibration when used with an AEM wideband AFR controller.