Two-dimensional model of the average course of the leads based on an example of an X-ray image in a PA projection (posterior–anterior). Distance measurements in cm; Angle measurements in degrees. (A) Midclavicular line—right; (B) Lateral sternal line—right; (C) Lateral sternal line—left; (D) Midclavicular line—left; (E) Upper clavicular line—left; (F) Lower clavicular line—left; (G) Upper clavicular line—right; (H) Lower clavicular line—right; (I) Diaphragm dome line. Red letters are explained in Appendix A, Table A1.