Big confusion relates to dBm, which is dB related to 1mW. Trouble is you need to know the impedance to work out what 1dBm is in volts (or mV or uV). I was once working in radio and added the input dBm to the dB of each stage to arrive at the final signal. Right? Nope! Wrong! The input signal was specified in dBm relative to 50 ohms and the audio out was in dBm relative to 600 ohms. Aaaarrrggghhhh!