ECG Paper ECG paper is designed to move through the ECG machine at 25 mm per second. Each of the smallest boxes are l mm square making the darker lined boxes 5 mm square. Thus, at the usual rate of 25 mm/second flow of the paper through the machine, 5 large boxes pass through the machine per second or (5 x 60 seconds) 300 boxes per minute.ECG paper
Time Scale each l mm represents 0.04 seconds. The distance between the darker lined boxes in a horizontal direction represents 5 x 0.04 seconds or 0.2 seconds. Therefore, 25 small boxes (5 large boxes) pass through the machine every second. One large box (made up of 5 small boxes) equals 1/5 (0.20) second.