An apparatus for determining a physiological parameter of a user, wherein the apparatus is a wearable device, and comprises: a first module in contact with or adjacent to an outer portion of a user's wrist, when the device is secured to the user; a second module in contact with or adjacent to an inner portion of the user's wrist, when the device is secured to the user; and a strap configured to secure the first module and the second module to a user's wrist, when the device is secured to the user, wherein the first module comprises a first sensor array on an inward facing surface of the module configured for contact with a first targeted area of the user and a second sensor array on an outward facing surface of the module; wherein the second module comprises a third sensor array on an inward facing surface of the module configured for contact with a second targeted area of the user; characterized in that the strap extends from the first module at an angle of between 5° and 15° with respect to a plane perpendicular to a longitudinal extension of the user's arm or wrist such that when it is secured to the user the circumferential extension of the strap lies in a plane that is not perpendicular to a line corresponding to the longitudinal extension of the user's arm, and the third sensor array is located proximate to a center of a radial artery of the user; the first sensor array and second sensor array each comprise one or more electrodes, the one or more electrodes of the first sensor array configured for contact at the user's arm to which the apparatus is secured and the one or more electrodes of the second sensor array configured for contact with a fingertip of the user on an opposing arm. a first module in contact with or adjacent to an outer portion of a user's wrist, when the device is secured to the user; a second module in contact with or adjacent to an inner portion of the user's wrist, when the device is secured to the user; and a strap configured to secure the first module and the second module to a user's wrist, when the device is secured to the user, wherein the first module comprises a first sensor array on an inward facing surface of the module configured for contact with a first targeted area of the user and a second sensor array on an outward facing surface of the module; wherein the second module comprises a third sensor array on an inward facing surface of the module configured for contact with a second targeted area of the user; characterized in that the strap extends from the first module at an angle of between 5° and 15° with respect to a plane perpendicular to a longitudinal extension of the user's arm or wrist such that when it is secured to the user the circumferential extension of the strap lies in a plane that is not perpendicular to a line corresponding to the longitudinal extension of the user's arm, and the third sensor array is located proximate to a center of a radial artery of the user; the first sensor array and second sensor array each comprise one or more electrodes, the one or more electrodes of the first sensor array configured for contact at the user's arm to which the apparatus is secured and the one or more electrodes of the second sensor array configured for contact with a fingertip of the user on an opposing arm. <EOS>