Is it possible to subtract two waveforms without a common reference or ground?

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juming
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Morning :)
I am trying to sample two different waveforms, and subtract the one from the other. Basically, I have A, B, and want C=A-B.
The device calculating the C=A-B is remote, connected to the two sampling A and B via a wireless link.
A and B do not have any common reference or ground, and the devices sampling them are battery operated.
Can I simply take the potential difference between A and a battery's negative terminal... and B and the next battery's negative terminal... and assume that the negative terminals are equal, such that I now have two waves that I can subtract from each other to get a proper difference between the two?
 

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It sounds like each floating wireless sensor is sending the amplitude of A and the amplitude of B. As such, they are stand-alone quantities, without any reference anymore. So yes, just do a simple arithmetic subtraction at the receiving end of the wireless link.