A method for noninvasively measuring analytes such as blood glucose levels includes using a non-imaging OCT-based system to scan a two-dimensional area of biological tissue and gather data continuously during the scanning. In certain embodiments, computing devices are mapped into different groups based on location information, and inter-group information is collected and used to identify other computing devices to which it would be efficient and effective for a computing device to send download requests for digital content. Content is protected at several levels, including: no protection; source-sealed; individually-sealed ; source-signed; and fully-individualized. A reference voltage is electrically connected to the positive node of the operational amplifier. The handheld tool with the tracking system and one or more sensors can be used to generate tracking data of the tool location and trajectory while measuring parameters of the muscular-skeletal system at an identified location.