Different electrode combinations allow more channels to be displayed than electrodes. Channels are commonly referred to as "leads," so there are 12 separate channels graphically displayed on a 12 Channel ECG Machine. The number of leads, depending on the form, ranges from 1 to 12. The wires that run to the electrodes are also occasionally called leads. http://www.zoncareglobal.com/ecg-machine/12-channel-ecg-machine/