Another technique is isolators, which can be transformer or optical. There are limitations such as imbalanced inputs, there is the concern of parasitic capacitance and very low common mode rejection ratio at high frequencies. An isolator is an accessory which allows oscilloscopes to safely make floating measurements. It consists of a conventional single ended oscilloscope front end (attenuator and preamplifier) protected with insulation which drives an isolation system based on either optical, transformer, or a combination of both systems. The output is a ground referenced amplifier that can connect to any oscilloscope, which remains safely grounded. The input probe is similar to a conventional attenuating scope probe, with better insulation in the ground lead to accommodate the higher reference voltages. Notice that there is no resistive path between ground and either input. There is still a capacitive element however, which will resonate with the inductance in the ground lead similar to a floating scope. This capacitance is much lower than that of the floating scope, so the effect is not as great.