An optical measurement device comprising: an illumination and detection assembly disposed on a printed circuit board and comprising a light emitting diode, LED , configured to output light to a surface portion of a user for measurement and a photodetector configured to detect the output light reflected from said surface portion of the user as a signal, the printed circuit board further comprising an opening disposed between the LED and the photodetector ; and a pressure detection assembly configured to detect an amount of pressure applied to the illumination and detection assembly by the user, the pressure detection assembly comprising a force sensor , the pressure detection assembly further comprising a force transmitting member including an opaque assembly piece and an opaque overhead portion , the opaque assembly piece extending through the opening in between the LED and the photodetector , so as to prevent light emitted by the LED from travelling directly to the photodetector , wherein the opaque overhead portion includes a first access hole for allowing light emitted from the LED to pass through and a second access hole for allowing reflected light to pass through to reach the photodetector , wherein the illumination and detection assembly and the pressure detection assembly are configured to communicate with a feedback unit that is configured to correlate a quality of the detected signal with the amount of applied pressure by: computing an area under waveforms of detected signals corresponding to a variety of applied pressure amounts, and determining an optimum pressure to correspond a largest computed area, from the variety of applied pressure amounts. an illumination and detection assembly disposed on a printed circuit board and comprising a light emitting diode, LED , configured to output light to a surface portion of a user for measurement and a photodetector configured to detect the output light reflected from said surface portion of the user as a signal, the printed circuit board further comprising an opening disposed between the LED and the photodetector ; and a pressure detection assembly configured to detect an amount of pressure applied to the illumination and detection assembly by the user, the pressure detection assembly comprising a force sensor , the pressure detection assembly further comprising a force transmitting member including an opaque assembly piece and an opaque overhead portion , the opaque assembly piece extending through the opening in between the LED and the photodetector , so as to prevent light emitted by the LED from travelling directly to the photodetector , wherein the opaque overhead portion includes a first access hole for allowing light emitted from the LED to pass through and a second access hole for allowing reflected light to pass through to reach the photodetector , wherein the illumination and detection assembly and the pressure detection assembly are configured to communicate with a feedback unit that is configured to correlate a quality of the detected signal with the amount of applied pressure by: computing an area under waveforms of detected signals corresponding to a variety of applied pressure amounts, and determining an optimum pressure to correspond a largest computed area, from the variety of applied pressure amounts. <EOS>