The 4431 RF Wattmeter is the same as the model 43 General Purpose Wattmeter with the addition of an RF signal sampler probe. This RF probe provides a low power sample of the signal being measured and is available at the female BNC connector on the right side of the housing. The signal level can be adjusted with a control knob on the front of the meter. The sampled output can be connected to any RF signal monitoring device such as a frequency counter, spectrum analyzer, or oscilloscope.