From the prerequisite that the frequency domain IP is equivalent to time domain IP,this paper discusses the requirements for precision of potential difference measurement when the IP response parameters must attain the necessary precision. The time domain IP does not require very high relative precision of potential difference, but the supply current is large and the equipment is cumbersome. The frequency-varying method needs very high relavtive precision of potential difference, which can hardly be attained when polarizability is low.The dual frequency IP can simultaneously measure dual frequency potential differences,and the value of potential diffetepce has very high relative precision, so that it can easily and satisfactorily meet the requirement for the precision.