A universal device poller (UDP) is being built for a metric to monitor in a...

Comprehensive and Detailed Explanation From Exact Extract:

The radial gauge display in the SolarWinds web console requires that the polled value from the OID is a numeric type that supports gauge visualizations (for example, a percentage or value with a defined minimum and maximum). If the OID returns data that does not fit these requirements—such as text, status, or a counter with no clear min/max—the gauge option will be grayed out and unavailable for selection. This behavior is explained in the Universal Device Poller documentation, which states that only compatible numeric OID types can be displayed using radial gauge resources.