I've seen similar circular wrenches used to set the elapsed time before a shell exploded and thus for ack-ack the height. The original from about the 17th century was a spiral set of dots on a shell fuse - the gunner pierced the required point for the time of flight so the shell burst over the taget. The old Priddy's Hard Museum near Fareham used to have a great display of old gunnery but it all got removed with the "update".