Improved
Bundle branch and fascicular blocks, marked step by step
Before
Study mode on the RBBB, LBBB, LAFB and LPFB pages lit each step's leads, but drew nothing on the tracing.
After
Every step is drawn on the tracing: the QRS and R-peak time callipers, the r, S and R′ of V1, LBBB's missing septal q and notched R, the q and S waves that turn the axis, and the ST and T pointing away from the QRS. Each step lights only the leads that make its point.