Precise Resistance Measurement Techniques
A common accurate method to resistance is the 4-point probe. The issue with a standard resistance measurement, using 2 probes, is that it uses the same contacts to deliver current and measure voltage. This means there is a voltage drop in the probes themselves (as well as contact resistance, but that isn't overcome with a 4-point). To get around this, 4 probes are used: 2 of them deliver current, the other two measure voltage.

This is commonly done using expensive bench-type multimeters, but can also be performed with 2 decent multimeters, a current source, and a pocket calculator. Use the current source to drop a voltage across the resistor in question, and measure this current with one meter. Beware that meters have a burden voltage, and often cannot measure low currents accurately (Dave Jones makes the uCurrent to combat this). With the other meter measure voltage drop across the resistor. Calculate resistance with your calculator with Ohm's Law: R = V/I. This method will be limited by your current meter's burden voltage. You'll find that it will give resistance measurements slightly lower than if you simply measure with 1 meter alone.

The 4-point probe technique is often used to characterize Si wafers, whose resistivity ranges from 10^12 to 10^18 Ωm!