Method for measuring conductance of a sample, the method comprising - providing a magnetically effective coil as a single ferrite cup core coil, an oscillator connected to the ferrite cup core coil and applying a voltage to the ferrite cup coil inducing a magnetic field, and providing an automatic gain control circuit connected to the oscillator whereby the automatic gain control circuit controls the output of the oscillator to the ferrite cup core coil; - measuring a voltage when the ferrite cup core coil is inducing a magnetic field in the absence of the ferrite cup core coil being positioned adjacent a sample such that the sample is not in the presence of the magnetic field; - positioning the ferrite cup core coil adjacent the sample to be measured; - subjecting the sample to a magnetic field produced by the ferrite cup core coil and detecting a change in voltage generated by the automatic gain control circuit when compensating for the amount of energy absorbed by the sample due to the presence of the sample in the magnetic field; - converting the voltage change to a conductance value for the sample; - providing a plurality of individual conductance values of the sample measured at a plurality of measurement locations, and comparing said individual conductance values to a plurality of respective standard conductance values; - wherein the change in voltage corresponding to each conductance value is relative to the voltage measured when the ferrite cup core coil is inducing the magnetic field in the absence of the ferrite cup core coil being positioned adjacent the sample; - and determining whether the conductance values of the sample are within a predetermined range. - providing a magnetically effective coil as a single ferrite cup core coil, an oscillator connected to the ferrite cup core coil and applying a voltage to the ferrite cup coil inducing a magnetic field, and providing an automatic gain control circuit connected to the oscillator whereby the automatic gain control circuit controls the output of the oscillator to the ferrite cup core coil; - measuring a voltage when the ferrite cup core coil is inducing a magnetic field in the absence of the ferrite cup core coil being positioned adjacent a sample such that the sample is not in the presence of the magnetic field; - positioning the ferrite cup core coil adjacent the sample to be measured; - subjecting the sample to a magnetic field produced by the ferrite cup core coil and detecting a change in voltage generated by the automatic gain control circuit when compensating for the amount of energy absorbed by the sample due to the presence of the sample in the magnetic field; - converting the voltage change to a conductance value for the sample; - providing a plurality of individual conductance values of the sample measured at a plurality of measurement locations, and comparing said individual conductance values to a plurality of respective standard conductance values; - wherein the change in voltage corresponding to each conductance value is relative to the voltage measured when the ferrite cup core coil is inducing the magnetic field in the absence of the ferrite cup core coil being positioned adjacent the sample; - and determining whether the conductance values of the sample are within a predetermined range.