teardown or theroy of electronically controlled resistance source [ohm source]

[croyleje]

hi everyone,

there is a discussion in general chat and the idea of seeing one torndown or at least Dave's ideas of how they work came up.  its a ohm source, found plans on line that basically use lots or relays to shunt precision resistor but I don't think that is how it is down.  would love to see in one and also think it would make a cool project would be nice to be able to type in needed resistance and out it comes.

http://www.tequipment.net/IETOhmSource.html

would like to know your thoughts Dave.

thanks

Jason