The present invention provides a personal hand-held monitor (PHHM) comprising a signal acquisition device for acquiring signals which can be used to derive a measurement of a parameter related to the health of the user, wherein the signal acquisition device comprises a blood photosensor having one or more photo-emitters for transmitting light to a body part of a user, one or more photo- detectors for detecting light transmitted through or scattered by the body part and two or more optical cells, at least one of which contains an analyte to be detected or which mimics the absorption spectrum of the analyte, through which the light that has been or will be transmitted through or scattered by the body part passes before it reaches the photo-detector(s), wherein the processor of the PHHM is adapted to process the signals received from the or each photo-detector to calculate the difference in intensity of light which has passed through the or each analyte cell and light which has passed through the or each non-analyte cell, to determine the pulse of the user and to correlate the signals obtained from the photosensor with the pulse of the user wherein the PHHM is adapted to apply pressure to the body part or to have pressure applied to it by the body part so that, in use, an artery in the body part changes from occluded to patent during each pulse and the processor of the PHHM is adapted to derive a measurement of the change in the luminal area of the artery during each pulse and to correlate the signals received from the blood photosensor with the pulse and the change in the luminal area of the artery to provide a measurement of the concentration of the analyte in the arterial blood.
