Electrical resistivity

I believe you're asking about something called a "Kelvin Connection," so correct me if I'm wrong. The advantage is that two conductors carry current to the material whose resistance is being measured (necessary condition for making DC resistance measurements -- V = IR, ya' know), the voltage drop in which doesn't matter, and two conductors measure the voltage drop through the material of interest at the points of contact from the current source. The current in the voltage probe conductors is nearly zero, so there is nearly zero error in voltage measurement.

I believe Keithley Instruments has published a book dealing with precision measurements, and I'm fairly sure it can be found on the internet.

Simple,

As in all Kelvin type probes, the use of 4 conductor probe zero's the probe's influence on the measurements. Especially important when measuring very low values, when probe's L, C or R values maybe close to the tested component values .

Ira Curtis- Wangito

I believe you are correct, but I believe the 4-point method also negates the contact resistance, which is not a probe or test-specimen property, per se, and can be sustantial in many cases.