Six landmarks, and how to find them

Every beat below is real, taken from the PhysioNet QT Database, and every boundary drawn on it was placed by a cardiologist. The shaded band is the tolerance you will be scored against in Practice.

Every figure below is the same beat, so you can see how the six landmarks sit relative to one another: record sele0166, beat 158571, lead D3. It is one of the fully annotated records, which is why it can demonstrate all six including the T onset.

Notice that the bands are not the same width. Expert cardiologists agree on QRS onset to within ±6.5 ms, but on the end of the T wave only to within ±30.6 ms. Some boundaries genuinely are harder to see than others, and the scoring reflects that rather than pretending otherwise.