It looks like you are using an external reference , as noted above , with the Arduino rather than the internal reference - what is it , how is it wired , why are you using it ?.
Using and passing current through a bread board is liable to cause voltage drops ( eg in the 0v lines ) which are reflected in your measurements .
You also need to check that doing a lot of maths on a analog signal does not loose the resolution of that signal , using floats, taking logs etc on a integer ( 1 part inn1024) derived signal creates warning signals.
Start simple and print out the raw analog values to see what’s happening