The Keysight X486A provides high efficiency and good match are characteristic of the X486A waveguide thermistor mounts. Used in conjunction with the 432A power meter, they provide high accuracy even in routine power measurements. These thermistor mounts are temperature compensated for low drift, even in the presence of thermal shocks, permitting measurement of microwave power as low as one microwatt. Each mount contains data showing calibration factor and effective efficiency at six frequencies, directly traceable to the U.S. National Institute Standards and Technology (NIST)at those frequencies where NIST provides calibration service.