a highly accurate electromagnetic - induction - type conductivity and dielectric constant meter is obtained by using a calibration box and a structure as below . the conductivity and dielectric constant meter employs an electromagnetic inductive probe which includes a primary transformer composed of a toroidal core with a wound primary coil , a secondary transformer composed of a toroidal core with a wound secondary coil , an electrostatic shield shielding the transformers , and cables that connect the probe to a meter . to eliminate the electrostatic capacity produced by causes other than electromagnetic induction , the structure of the probe is symmetrical . in a first embodiment , the secondary transformer is placed between two parts of the primary transformer , which has two cores of the same shape that are placed symmetrically . the structure , including the primary and secondary transformers , gaps in the electrostatic shields , and cables , are symmetrical with respect to a plane perpendicular to the central axis of the ring shapes and passes through the center of the annular core of the secondary transformer .