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 to be detected, through which the light that has been or will be transmitted through or scattered by the body part passes before it reaches the or each photo-detector, 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 and to process signals obtained from the photosensor to provide a measurement of the concentration of the analyte in the user's blood, wherein either: ⋅ the or each photo-emitter is a light-emitting diode (LED)； ⋅ an optical cell that mimics the absorption spectrum of the analyte to be detected is used and is a manufactured optical filter； ⋅ the PHHM is adapted to provide optical signals at one or more additional wavelengths for transmission to the body part, and the processor of the PHHM is adapted to process signals at the or each additional wavelength to estimate the volume of blood in the field of view of the blood photosensor； or ⋅ there is a ridge on the surface of the signal acquisition device between the photo-emitter(s) and the photo-detector(s).
