I get about 25mV of change from unloaded to fully loaded, so 0 - 50mV between green and white. On second thought that would only be 10 values using the arduinos ADC, so you would indeed have to amplify it. I don't know what the difference between a differential and an instrumentation amp is, but I don't see why a simple differential amp between the green and white wires wouldn't work. I didn't test how the voltages correspond to weight applied but I'm guessing it's non-linear.