Upper potentiometer is Negative Input, Lower pot is Positive Input. This circuit was absolute hell to get working properly, but here goes! Op Amps mainly seek to amplify the differences between the positive and negative inputs and reject common signals between the two inputs. They typically consist of a differential pair of transistors sourced by a current mirror (or other active load). The diff pair is sinks to a nMOS current mirror that also serves to bias the output voltage and allow the output to saturate to both the low and high voltage rails. This is only my best understanding of the circuit so far, so do your own research and take my words with a heavy grain of salt! I'm still having trouble getting feedback to work properly as it would in a standard op amp.
