I'm measuring it at the input into the Arduino and to the common ground the Arduino and every circuit shares; so physically, right at the analog pin into the Arduino after the division circuit(s). I also read the impedance reading for every known resistor in my 16 circuits and they are all within tolerance of 1%.
Is this referencing @Koepel's suggestion of ground currents? If so, I've already clarified that I've read no voltage on the ground which would also imply no current. This is consistent with both a multimeter and calibrated fluke (just to remove the suggestion that the multimeter could be imprecise).