How to buy a cardiograph?12 Channel 3 or enough?

Is there a significant difference between the two?I just look at almost all the patients, making ECG - at them on paper in all three graphs at the same time go.Then both are on the same tape again 3 graphics, but other leads, it turns out the rules?

But probably better immediately when removed 12 leads?I'm just not super rummage in ECG, wanted to buy a home, and I think three or 12 need be limited.Just do not know whether the unit to record 3 standard leads, and then remove the 3 leads in other parts of the body