A Universal/Upgrading Pulse Oximeter (UPO) comprises a portable unit and a docking station together providing three-instruments-in-one functionality for measuring oxygen saturation and related physiological parameters. The portable unit functions as a handheld pulse oximeter. The combination of the docked portable and the docking station functions as a standalone, high-performance pulse oximeter. The portable-docking station combination is also connectable to, and universally compatible with, pulse oximeters from various manufacturers through use of a waveform generator. The UPO provides a universal sensor to pulse oximeter interface and a pulse oximetry measurement capability that upgrades the performance of conventional instruments by increasing low perfusion performance and motion artifact immunity, for example. Universal compatibility combined with portability allows the UPO to be transported along with patients transferred between an ambulance and a hospital ER, or between various hospital sites, providing continuous patient monitoring in addition to plug-compatibility and functional upgrading for multiparameter patient monitoring systems. The image on the portable display is rotatable, either manually when undocked or as a function of orientation. In one embodiment, the docking station has a web server and network interface that allows UPO data to be downloaded and viewed as web pages over a local area network or the Internet.