Also known as: 計量器, けいりょうき, 計器, けいき
An instrument that displays a measurement (of pressure or temperature, for instance) by moving a needle across a scale.
Examples of these can be found on post #1483841 (strapped to the girl's thigh) or post #1665641 (on the front of the aircraft). These sometimes take the form of a thermometer-like measurement bar, or a Dial.
For video game interfaces that indicate energy, health, progress, etc., see Health Bar.
For the wide-diameter piercings colloquially called "gauges", see Plug (Piercing).