[header] How to read an ekg [title] Understand the grids of an ekg paper printout. [step] Voltage-the electrical signals of the heart-is measured along the vertical axis; time is measured along the horizontal axis in squares. There are large squares that are divided into smaller squares. 
[substeps] Small squares are 1 mm across and represent 0.04 seconds. The large squares measure 5 mm across and represent 0.2 seconds.