2007 GMC Sierra 1500 Pickup Owner's Manual - Page 184

If your vehicle is equipped with this style trailering-type mirror, they can be adjusted so you can have a clear view of the objects behind you. Adjust each mirror by turning it left or right. Once the mirror is adjusted to the correct position, tighten the set screw to hold the mirror in place. These mirrors can also be manually folded in. On the lower portion of the mirror is a convex mirror. A convex mirror's surface is curved so you can see more from the driver's seat. If your vehicle is equipped with this trailer towing type mirror, they can be adjusted so you can have a clear view of the objects behind you. Pull out the mirror head to extend it for better visibility when towing a trailer. These mirrors can also be manually folded in. On the lower portion of the mirror is a convex mirror. A convex mirror's surface is curved so you can see more from the driver's seat. 184