The Resistivity Correction Factor (RCF) is changed with the sample shapes and sizes as well as measuring positions.

In the 4-pin probe method, since the sample size or measuring position are not fixed, the electric energy distributed in the sample is changed with the sample size and the measuring positions. If the sample size is small or the measuring position is near the sample edge, the peak of the electric field becomes higher to yield a high resistance. This is caused by the electric energy being contained in the sample.

The correction factors RCF (S) and RCF (V) of the ring electrode probe are determined by the electrode diameters. Correction factors of probes is registered previously in Hiresta-UX. Therefore the value can be called up automatically by selecting a probe type.

The Resistivity Correction Factor is used to obtain correct values for the volume or surface resistivity by forecasting such difference in the peak of the electric energy. The electric potential Φ(r) in an optional point in a sample and is calculated by solving a Poisson’s equation under a specific condition.

**Poisson‘s Equation ∇2 Φ(r) = 2 ρv I [ δ (r-rD) – δ(r-rA)]**

The Loresta-GX has a built-in software for calculating this factor and is able to derive the factor by simple input of the sample shapes (rectangular or disk) and size as well as the measuring position. The Loresta-AX uses a fixed RCF which allows a sufficient precise measuring.

The 4-pin probe method was included to the JIS K7194 (Japanese Industrial Standard) in 1994.