I learned in high school the basic rules of how to compute resistance between two points, given a network of resistors. You try to rearrange the circuit so into parallel parts and series parts, then compute the resistance of each piece individually using those rules, until you're left with just one number, and you're done. Maybe I explained that poorly, so consider the following schematic:
Sorry it's so large, that seems to be the default.
Anyway, it's easy to compute the resistance from A to D (regardless of the values of the all the resistors)- A-B-D, A-D, and A-C-D are all series connections (easy to compute) then you combine them with the parallel formula and you're set.
How do you compute the resistance from B to C? There seem like lots of possible ways to think about it, and they all generate different answers. I've left the specific numbers off the diagram because this isn't homework and I don't care about the answer specifically, I just want to understand the principles involved and how to solve the problem.
Any help, or links to especially readable guides, would be very much appreciated.