Graph ECG paper is divided into vertical and horizontal lines. The larger squares are 5mm. The time or rate is estimated by measuring the number of square blocks along the horizontal line. The distance across one small square is 0.04 seconds. Vertical lines measure amplitude or voltage and is measured in millivolts.
Horizontal lines measure time.
Vertical lines measure voltage A one second strip consists of 5 large blocks, three seconds equates to 15, six second equates to 30. Begin by counting the R waves in a six second strip. Multiply that number by 10 to determine the heart rate in one minute. Quick count Count the large blocks that fall between two R waves. Start by finding an R wave that falls on or close to a dark line.