GE Marquette for HSI At the beginning of the electrocardiogram recording, the electrocardiograph automatically performs a calibration. An electrical 1 mV signal is sent for 0.2 s, recording a rectangular shape with a 10 mm height and 5 mm width on the graph paper (see image on the right). This image let us know the calibration used during the recorded EKG. As we previously mentioned, paper speed or amplitude can be adjusted in cases where the QRS voltages are either too high or too low. This would mean a different calibration, and therefore, a change in height or width of the calibration mark.