20 microns then the angular velocity is set to a value such that the focused beam 611 does not move laterally more than 200 microns during the depth scan by setting the angular velocity of each wedge prism 605 to such a value the distortion in the depth scale of each scan produced by the change in thickness of the wedge prism 605 as it rotates is minimized the threshold trigger depth scan rate and angular velocities are presets that may be optimized and built into the sensor system 601 at step s 806 the patient sets the sensor system 601 to begin scanning the skin 610 since a threshold trigger was set at 45 db in step s 804 the sensor system 601 will not accumulate scan data until the intensity of the optical signal produced by the sensor system 601 reaches a value of 45 db preferably the threshold is above the highest noise peak produced by the signal but at least 10 db lower than the intensity peak at the interface between the skin 610 and the disposable apparatus 614 once the sensor system 601 has completed taking multiple scans preferably around 1500 scans at step s 807 the sensor housing 614 may be removed from the disposable apparatus 608 or alternately the sensor housing 614 may remain and begin to take another glucose reading the disposable apparatus 608 remains adhered to the patient 39 s skin 610 the scan data.