An aspect of the disclosure pertains to a wrist-worn device that may be characterized by the following features: an external surface that is not in contact with the user when the wrist-worn device is worn； a force sensor； a PPG sensor disposed on the wrist-worn device； and control logic configured to: (i) generate one or more sensor data samples, each sensor data sample including data that links force data generated by the force sensor when a user presses a against the external surface at a given time with heart rate data obtained from the PPG sensor at the given time； and (ii) calculate an estimate of blood pressure from the one or more sensor data samples. As examples, the force sensor may be a force sensitive touch screen or film, a strain gauge integrating into the device, or a calibrated spring element configured to be pressed by the user.
