The Calendar Wheel is an agent included with the Dustdevil Grendels agent pack. In a C3-only or docked world, it injects into the Ettin Desert; in a DS standalone world, it injects into the Norn Meso.
The Calendar Wheel shows the current season, as well as the day of the season and roughly the time of day (early morning, middle of the day, or late evening). The top of the outer wheel shows the current season - storm clouds for spring, a sun for summer, an owl for autumn, and a bat for winter. The top of the inner wheel indicates the day and time of day - one dot for each day of the season, with the dots themselves representing the middle of the day, the rising sun next to it representing morning, and the moon next to it representing evening.