• The subject should lie flat on his/her back on a bench or cot, with hands at their sides.

• The inner aspect of the right forearm just above the wrist is rubbed briskly with alcohol.  A small drop of electrolyte paste is squeezed onto a plate electrode and is spread evenly over the surface of the electrode.

• The electrode is then placed onto the cleansed area, and secured to the arm using the rubber strap provided.

• The above is repeated for the left arm, and then for both legs, attaching the electrodes a few inches above the subject's ankles.

• LA (black plug) to plate on left arm
• RA (white plug) to plate on right arm
• LL (red plug) to plate on left leg
• RL (green plug) to plate on right leg

• The ECG/EMG switch on the ISO-1 is set to ECG.   The gain control is turned to about mid-position.  Lead II is selected on the lead-selector switch.

Remember that the potential measured at the right leg (VRL) is used as the reference potential. 

The connections for all three standard limb leads are shown to the left below.  The figure to the right shows a diagrammatic representation of the Einthoven Triangle Hypothesis. Willem Einthoven (1860-1927) attempted to explain the principles of the ECG in scientific terms.  In Einthoven's triangle, the heart may be considered to lie at the centre of an equilateral triangle and the corners of the triangles are the effective sensing points - the right arm, left arm and left leg.

Einthoven's Triangle