You searched for: “unipolar electrocardiogram
unipolar electrocardiogram
1. An electrocardiogram taken with the exploring electrode placed on the chest over the heart or upon a single limb, the indifferent ("zero" potential) electrode being the central terminal.
2. An electrocardiogram that shows the potential detected by a single electrode.

In practice, this is obtained by using an exploring electrode and a second electrode; such as, a central terminal that is assumed to have zero potential.