Keithley 6430 Quick Results Manual page 44

Offset-compensated
Thermal EMFs can corrupt low-resistance measurements. An offset-compensated 
measurement cancels out unwanted offset by performing the following 2-point
measurement process:
Offset-Compensated  = V / I
where: V = V2 - V1
I = I2 - I1
V1 and I1 are V and I measurements with the source set to a specific level.
V2 and I2 are V and I measurements with the source set to a different level (typically
zero).
Select the desired source function (V or I), and use the following menu sequence to
configure and enable the offset-compensated  math function:
Press CONFIG > press FCTN > select OFF COMP OHMS
After selecting OFF COMP OHMS, you will be prompted to enter the two source values.
This math function can now be selected by pressing the FCTN key.
Offset-compensated  is also available from the CONFIG OHMS menu. Using
NOTE
offset-compensated  from this menu automatically selects zero as one of the source
values. For details, see "Measure ohms" in the "Basic SourceMeter operations"
section of this guide.
Voltage coefficient
High value resistors exhibit a change in resistance with a change in applied voltage. The
voltage coefficient is the percent change in resistance per unit change in applied voltage:
R
Coefficient % = --------------------- -
R2 V 
where: R = R2 - R1
V = V2 - V1
R1 and R2 are the resistance measurements at the two source points.
V2 and V2 are the voltage measurements at the two source points.
After selecting the desired source function (V or I), use the following menu sequence to
configure and enable the voltage coefficient math function:
Press CONFIG > press FCTN > select VOLT COEFF
After selecting VOLT COEFF, you will be prompted to enter the two source values.
This math function can now be selected by pressing the FCTN key.
Quick Results Guide 37