For centuries, medical practitioners had no electronic medical instruments and had to rely on their senses of sight, hearing, smell, taste, and touch to obtain physiologic measurements. Although it is possible to estimate blood pressure by palpating the pulse at the radial or brachial artery, such estimates are not accurate. Determining arterial oxygen saturation of hemoglobin is more complex: how “blue” a patient appears depends on skin coloration, lighting, and the examiner's sense of color. Finally, using radiographic images to validate pulmonary edema when clinicians suspect that there is an elevated left atrial or pulmonary artery wedge pressure also challenges human senses. However, today's medical instruments use transducers and signal processors to convert patient information into a form that clinicians can easily perceive and understand. This article defines terms used with biomedical instrumentation and discusses the components of ideal physiologic patient monitoring systems