The Bridge Circuit

So I've been studying and trying to understand electronics for a week or so now, and I'm making some good progress. I now understand that voltage is directly related to both current and resistance and that current and resistance are inversely related. This is the foundation of all electronics.

The first 200 pages of the text book I'm plowing through don't cover a whole lot of practical applications for circuits, so I've got this knowledge of how to deliver certain voltages and calculate resistances but who cares?

One thing I desire out of this latest endeavor is to do soemthing that Tesla did, and that's contemplate an invention in my head. I can do such things readily with a complex plot line for a story or campaign, and I figure what I need to do the same with electronics is to become as steeped in electric lore as I am in roleplaying lore. The main driving force behind this study is to gather electronic devices to play with as I go about my daily business.

Then the authors (Russell L. Meade and Robert Diffenderfer) busted out a simple circuit design that has begun to satisfy this urge- the bridge circuit:

It took me a while to be able to comprehend this diagram, but let me pontificate on its uses. The V is a meter that tells the difference in voltage between the Rx-B-R3 leg and the R1-C-R2 leg. If R2 and Rx are the same value, then no voltage flows and the meter is at zero. Different resistive differences cause the voltage meter to go in either direction.

Basically, this is a sensor measuring Rx. Practically mounted, V would be your display and R2 your calibration knob. Rx would be some type of instrument with an electrical state sensitive to what is being sensed. Depending on how R2 is set, V displays how the sensor instrument differs.