<prompt> Einthovens triangle, what is the value of lead III when lead I 2 mv and Lead II 1 mv1234  <response>: Einthovens formula states that the sum of voltages from lead I plus those from lead III minus those from lead II is zero. Lead IIII-II0 This is based on the principle that the sum.of the voltages in a closed path equals zero. Because the positive and negative electrodes of lead II are reversed. So it is subtracted instead of adding. 