System for calculating ECG

Present disclosure relates to a system for calculating ECG. The system at least includes a first obtaining device, a second obtaining device, a third obtaining device and a mobile device. Each of the obtaining devices includes a first electrode, a second electrode and a processor. The three obtaining devices are placed on three limbs of a user respectively. The three obtaining devices are configured to obtain three sets of voltage variations between each two of the three limbs and record three time stamps corresponding to the obtainment. The three sets of voltage variations and three time stamps are sent to the mobile device. The mobile device is configured to calculate a substantially synchronized three leads ECG according to the three sets of voltage variations and the three time stamps.