This is a test of commonsense. Complete the next sentence:

How to read an ekg
Understand the grids of an ekg paper printout.
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.
Small squares are 1 mm across and represent 0.04 seconds. The large squares measure 5 mm across and represent 0.2 seconds.