the technique is used in equipment such as ecgs, sensitive photomultipliers, electrostatic sensors, and precision low-current measurement where leakage current would alter the measurement. any situation in which the source to be measured has a very high output impedance is vulnerable to leakage current and if sufficient insulation is not practical then a driven shield will improve performance. coaxial cable is well suited for use as a guard; if electromagnetic shielding is also required then triaxial cable should be used as depending on the type of buffer circuit any noise on the guard may be amplified in the output.