N231YE From , joined Dec 1969, posts, RR: Reply 3, posted (6 years 8 months 4 days 6 hours ago) and read 3719 times:
The extension is used as a tool to measure 90º and 45º angles with references to the horizon. Basically, aerobatic pilots, such as Patty Wagstaff, use these devices when they are "maneuvering" (as in stunts).
Quote: Each wingtip has a sighting device to aid in precision maneuvering.
The pilot simply looks to the side, out at the wingtip device, and can align either the 45 or 90 degree bar (and thus, the fuselage) with the horizon. One of the problems with the device is that, on hazy days with no discernable horizon, there is no point of reference, and the device is useless.