Referential montages are only as good as their reference electrode. The reference electrode is intended to be distant from the potential focus and inactive, but sometimes it may be very active. This is called an active reference; it misleads the reader into false localization. An active reference occurs if the reference electrode lies close to the potential focus or becomes contaminated by artifactual potentials. If the reference is at or near the focus, typically there is a unidirectional reflection (often with varying amplitudes) in all the channels. If the reference is contaminated by an artifactual potential, typically there is a phase reversal over channels that overlie a potential focus. Central references are prone to contamination with sleep potentials and ear references are prone to contamination with EKG and temporalis artifact. Switch to an alternative referential montage if you suspect an active reference. This is easy with a digital display.