Thanks for the response Janne,
I want to be able to record the voltage between the devices ground and signal outputs (so I would have two bits of information, a comparison of each output to ground). I am unable to get the arduino to record both and just subtract the difference because the device ground is about -1V compared to arduino ground the A/D reads 0 (it only works from 0-5V relative to arduino ground). Essentially I want to offset the difference.
This could be what I'm looking for
I haven't used these before so they're a bit of a mysterious black box to me. This from the datasheet look promising:
The reference terminal potential defines the zero output voltage and is especially useful when the load does not share a precise ground with the rest of the system. It provides a direct means of injecting a precise offset to the output.Just to be sure though, if I set this to a gain of 1 (by not connecting a resistor between +Rg and -Rg) and made the REF my arduino ground, -Vs = arduino ground, +Vs = arduino +5V, -IN = device ground, +IN = device signal then the voltage between OUTPUT and REF would be the same as the voltage between -IN and +IN?