Oh ok, that's nice! What I need than is a resistor ratio of 10 or more. I thought the inputs also influenced the gain."Vout= -R2/R1 (V2-V1)"
The output is the ratio of the resistors multiplied by the bit in brackets. This is the difference between V2 and V1. So 1V and 1.!V will give the same output as 3.3V and 3.4V. That is the magic of that circuit.
Thanks, i will look that up. I didn't know i had to take that into consideration as well.You might need to null any intrinsic offset of at least the first stage opamp.