The Linear Gauge is one of the flavours that are available in the RadGauge control family. It represents the value on a linear scale much like a thermometer would.
The specific properties that make it different are mostly related to the pointer - it can be either a small triangular tick (similar to an arrow), or an entire bar like a thermometer. It can be either horizontal or vertical.
This demo shows the basics of the Linear Gauge control. Examining the code will show the basic markup - tags and properties, the code-behind logic will show the code structure.
Some logic is incorporated for the configurator to keep the gauge appearance when changing properties. Also, setting a value that is outside of the range will result in either a min or max value being set, if you disregard the instructions in the value textbox before clicking the configure button.