AEM X-Series Wideband Gauges and the X-Series Inline Controller support the popular 4.9LSU sensor and offer both factory calibration resistor and free-air calibration methods. Factory resistor calibration provides precise calibration when the sensor is new, while free-air calibration can help correct drift as the sensor ages. AEM Wideband UEGO (Universal Exhaust Gas Oxygen) Controllers are powerful, cost-effective tuning tools that accurately monitor engine Air/Fuel Ratio (AFR). Accurate AFR data is critical for tuning because running rich can reduce power, while running too lean may cause serious engine damage. The UEGO sensor connector should not be modified because it contains a laser-etched calibrated resistor specifically created for the attached sensor; modifying it will invalidate the sensor's output. Independent testing by 360° Product Testing, reported August 31, 2015, against 17 competitor wideband UEGO Air/Fuel Controllers found the AEM X-Series Inline with 4.9LSU sensor and X-Series Wideband UEGO AFR Gauge with 4.9LSU sensor recorded the fastest response times. Wideband UEGO sensors are wear items affected by leaded fuel, automotive fluids, particulates, mechanical or thermal shock, and being unheated while exposed to exhaust. Free-air calibration may correct drift, but sensor replacement as part of regular vehicle maintenance is recommended. Follow the instruction manual when performing free-air calibration. Display Gasoline and OBDII Gasoline: 8.0:1-20.0:1 AFR; Display and OBDII Lambda: .55-2.00; 0-5V Gasoline: 8.5:1-18.0:1 AFR; 0-5V Lambda: .58-1.23; 0-5V E85: 5.7:1-12.0:1 AFR; 0-5V Ethanol: 5.2:1-11.0:1 AFR; 0-5V Methanol: 3.75:1-8.0:1 AFR. 0-5V outputs require wiring.