Experimenting

An experimenter in a facebook group that I'm a member of put up the following schematic. They asked for group members' help to give a simple explanation of the circuit. I've put the schematic here, so that I can give some feedback with a little space and some links.



The above circuit is a fluid level meter that converts the level in the container on the left into a single-digit number, from 0-9 on a seven-segment display. In this case, 0 (zero) represents the lowest level, and 9 (nine) is the highest level.