I looked up the history and the technology in the book stores and the web, but still having trouble getting an exact fix on how depedable this old ecg/ekg technology really is. Seems doctors have a great deal of confidnece in them, though. I would still like to hear several professionals opinions, and counter-opinions(accademic) of the strengths and weaknesses of this technology. I searched for weaknesses on Pub Med and found some suggestions that subcutaneous fat, isotropic muscle(scar tissue?), lungs, and even slight missplacement of these V-probes can cause problems or errors, but I'm not so sure how common or reliable the research was. Still searching and still learning...slowly.