Adjustable body monitoring system comprising: - a main body adapted to measure a physiological quantity of a user, - a wristband configured to surround a limb of the user, the strap comprising a first strap mounted on the main body and a second strap mounted on the main body, the first strap comprising a one-dimensional array of notches, the one-dimensional array of notches having a pitch p, the second strap comprising fastening means configured to be removably secured in one of the notches, each notch forming an opening through the first strap, wherein - a first face of the first strap comprises a plurality of markers, each marker being formed by a relief or a variation in color between the surface of the marker and the rest of the first face, a portion of each marker being arranged at a distance less than or equal to the pitch p of a notch associated with said marker, preferably at a distance less than half the pitch p of the associated notch, so as to form a first one-dimensional array of markers, two adjacent markers of the first one-dimensional array of markers having different shapes and/or different colors reflected by the first face, and/or different main orientations in the spatial reference frame of the first strap, - a second face of the first strap opposite the first face, comprising a plurality of markers, each marker being formed by a relief or a variation in color between the surface of the marker and the rest of the second face, a portion of each marker being arranged at a distance less than or equal to the pitch p of a notch associated with said marker, preferably at a distance less than half the pitch p of the associated notch, so as to form a second one-dimensional array of markers, two adjacent markers of the second one-dimensional array of markers having different shapes and/or different colors reflected by the second face, and/or different main orientations in the spatial reference frame of the first strap. - a main body adapted to measure a physiological quantity of a user, - a wristband configured to surround a limb of the user, the strap comprising a first strap mounted on the main body and a second strap mounted on the main body, the first strap comprising a one-dimensional array of notches, the one-dimensional array of notches having a pitch p, the second strap comprising fastening means configured to be removably secured in one of the notches, each notch forming an opening through the first strap, wherein - a first face of the first strap comprises a plurality of markers, each marker being formed by a relief or a variation in color between the surface of the marker and the rest of the first face, a portion of each marker being arranged at a distance less than or equal to the pitch p of a notch associated with said marker, preferably at a distance less than half the pitch p of the associated notch, so as to form a first one-dimensional array of markers, two adjacent markers of the first one-dimensional array of markers having different shapes and/or different colors reflected by the first face, and/or different main orientations in the spatial reference frame of the first strap, - a second face of the first strap opposite the first face, comprising a plurality of markers, each marker being formed by a relief or a variation in color between the surface of the marker and the rest of the second face, a portion of each marker being arranged at a distance less than or equal to the pitch p of a notch associated with said marker, preferably at a distance less than half the pitch p of the associated notch, so as to form a second one-dimensional array of markers, two adjacent markers of the second one-dimensional array of markers having different shapes and/or different colors reflected by the second face, and/or different main orientations in the spatial reference frame of the first strap.