Linear Gauges are simulators of real gauges with an only measurement to demonstrate. It basically uses a minimum set of charting elements like labels, as there is almost no sense in using tooltips or legend if you need to show, for example, a battery charge level. Though, the gauges can be more complicated, like the example above.
This example contains four linear gauges of tank pointer type. Each shows the volume amount of one of the substances (water, oil, sugar or coffee) in ml in a kilogram. Hover a pointer to see the tooltips and get the exact information about the substance it represents: its name and its volume in ml in a kilogram. Also, below the title of the chart, you can find a legend, which helps to manage the gauges, turning them on and off.