Have you ever tried to draw the Einthoven's triangle & every time wondered where to put the +ve or -ve sign and which are the leads I, II & III? Here is an easy way to draw it.

First, lets see the picture below & identify the three Poles (RA, LA & LL) and three leads (I, II & III). Also see the +/- signs at each pole.




Each pole will have two signs (either +/-, +/+ or -/-). The number of '+' signs will be equal to the number of  'L' at that pole. So,
RA = -/-
LA = +/-
LL = +/+

The lead number between two poles will be equal to the number of combined 'L' of the two poles. So,
Lead between RA &  LA = Lead I (only one L)
Lead between RA & LL = Lead II (two L)
Lead between LA & LL = Lead III (three L)