I've used the built in HRM on the computrainer while I've had my regular one on too (a Sigma) and they have not always agreed exactly. In general they were pretty close, but the Sigma would react faster and, I think, was more accurate overall (Sigma also makes ECG equipment for hospitals... they say their consumer products are just as accurate). The computrainer one was often a little lower or a little higher and definitely had some lag time before it catch up to a hr change.