An unwanted portion of the total [[conductivity]] [[signal]] sent to the surface by the downhole [[induction log|induction-logging]] instrument. The sonde error is generated by imperfections in the coils in the sonde. It is isolated and measured during the [[calibration]] operation when the sonde is placed in a zero signal medium (air). Once evaluated, it is cancelled during the [[survey]] operation. See also [[diode error]].