Systems, methods, and devices for obtaining consistently reproducible diagnostic measurements with a photoplethysmographic sensor are provided. In one embodiment, a method for obtaining such a diagnostic measurement includes applying a pressure between a photoplethysmographic sensor and a patient, increasing the pressure until the photoplethysmographic sensor outputs a plethysmographic waveform of minimal amplitude, decreasing the pressure by a predetermined fraction, and obtaining a diagnostic measurement using the photoplethysmographic sensor. The pressure may be applied using a pressure device that includes, for example, a clip, a wrap, an inflatable balloon or bladder, or an inflatable cuff or any combination thereof.