A method and apparatus for easing the use of an optically based noninvasive analyzer is presented. More particularly, a simplified algorithm is used that removes the daily requirement of collecting and using a noninvasive spectrum to update a calibration model. In another embodiment, a guide is used to substantially reduce variation in sample probe placement in relation to a skin tissue sampling site, resulting in the ability to maintain calibration performance with the use of a reference analyte concentration, with or without the use of a reference spectrum collected nearby in time.