An electrocardiogram (ECG) sensing device , comprising: a mobile phone or a wearable computing device , the mobile phone or the wearable computing device being operatively coupled with a first electrode , a second electrode , and a third electrode ; a processor; and a non-transitory computer readable storage medium encoded with a computer program including instructions executable by the processor that causes the processor to: generate six limb leads of the ECG including a first lead I waveform based on electric potential differences sensed between the first electrode , the second electrode , and the third electrode when each is respectively contacted by a user's left hand, right hand, and left leg; determine a Wilson's Central Terminal (WCT) value using two of the six limb leads; generate one or more of the precordial leads of the ECG based on a difference between an electric potential sensed by the third electrode and the WCT value when the third electrode is contacted by the user's chest, and simultaneously generate a second lead I waveform based on an electric potential difference sensed between the first electrode and the second electrode when the first electrode and the second electrode are contacted by the user's left hand and right hand while the third electrode contacts the user's chest; and time align the six limb leads and the one or more precordial leads using the lead I that was simultaneously generated with the one or more precordial leads. a mobile phone or a wearable computing device , the mobile phone or the wearable computing device being operatively coupled with a first electrode , a second electrode , and a third electrode ; a processor; and a non-transitory computer readable storage medium encoded with a computer program including instructions executable by the processor that causes the processor to: generate six limb leads of the ECG including a first lead I waveform based on electric potential differences sensed between the first electrode , the second electrode , and the third electrode when each is respectively contacted by a user's left hand, right hand, and left leg; determine a Wilson's Central Terminal (WCT) value using two of the six limb leads; generate one or more of the precordial leads of the ECG based on a difference between an electric potential sensed by the third electrode and the WCT value when the third electrode is contacted by the user's chest, and simultaneously generate a second lead I waveform based on an electric potential difference sensed between the first electrode and the second electrode when the first electrode and the second electrode are contacted by the user's left hand and right hand while the third electrode contacts the user's chest; and time align the six limb leads and the one or more precordial leads using the lead I that was simultaneously generated with the one or more precordial leads. generate six limb leads of the ECG including a first lead I waveform based on electric potential differences sensed between the first electrode , the second electrode , and the third electrode when each is respectively contacted by a user's left hand, right hand, and left leg; determine a Wilson's Central Terminal (WCT) value using two of the six limb leads; generate one or more of the precordial leads of the ECG based on a difference between an electric potential sensed by the third electrode and the WCT value when the third electrode is contacted by the user's chest, and simultaneously generate a second lead I waveform based on an electric potential difference sensed between the first electrode and the second electrode when the first electrode and the second electrode are contacted by the user's left hand and right hand while the third electrode contacts the user's chest; and time align the six limb leads and the one or more precordial leads using the lead I that was simultaneously generated with the one or more precordial leads. <EOS>