In one embodiment of the invention, a non-invasive method of measuring blood pressure is disclosed. The method includes scanning for ECG data with a portable cuffless blood pressure measuring device including, forming an electronic circuit with a first electrode and a second electrode of the portable cuffless blood pressure measuring device by contacting the first electrode with a user's temple and contacting the second electrode with the user's finger holding the portable cuffless blood pressure measuring device; concurrently scanning for PPG data with the cuffless blood pressure measuring device during ECG scanning by placing the PPG sensor to the user's temple; cross-correlating the ECG data and the PPG data to determine a PWTT for the user; receiving one or more physiological data of the user; and using regression analysis to predict systolic blood pressure of the user in response to the PWTT and the one or more physiological data.