impedance bridge, which one is better?

betwixt said:

The actual output impedance is complex and will vary considerably with frequency, particularly the monitor output. The impedance of the DC output will be more than 10K at low frequencies by virtue of the resistor but in both cases the 1nF capacitor will drop the impedance at high frequencies. What is important is that the outputs are not unduly loaded because they will not provide much current. Adding a load resistance will help the capacitors at the ports discharge but 100K should be low enough. My point was that if you use op-amps, pick a type with a FET input stage so it's input current requirement is very low.

Brian.

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I will probably use a resistor divider to convert the negative voltage to positive, like described here https://www.edaboard.com/threads/285737/#post1224998 I like this solution, provided that the vcc is stable and the resistors are of low ppm I believe greater accuracy can be achieved without the temperature variation problems. Of course you have some voltage loss from the divider but in my application comparative readings have to be made and not actual. More important, is the immunity to variations of the measuring equipment, to ensure that the same readings will always represent the same values.
Having that in mind, I would like to make a potential divider but I do not know the short of resistor values to use, that is why I am asking about the impedance at the monitor and dc out ports.
Any suggestions will be appreciated.