A tagging system (20) compensates for both resonant frequency spatial dependent shifts and resonant frequency dependent shifts for detecting data resonant circuits (DC1-DC6) on an RF tag 10 which is carried by a tagged object (34). The system includes at least one transmitter (26) and at least one receiver (28) for determining the actual resonant frequencies of reference resonant circuits (SC1-SC5, FC1-FC4) on the tag 10. A microprocessor controller (22), in response to the frequency difference between the undisturbed resonant frequencies of the reference resonant circuits and the actual resonant frequencies of the reference resonant circuits, provides compensating factors to compensate for the spatial and frequency effects of the resonant frequencies of the resonant circuits on the tag (10). The transmitter and receiver determine the actual resonant frequency of each data resonant circuit (DC1-DC6) on the tag (10). The microprocessor controller (22) then determines the undisturbed resonant frequencies of the data resonant circuits on tag (10) from the actual resonant frequencies of the data resonant circuits and the compensation factors.