Starting with W, we have the Wedge Plate on page 155 — Page 665, Lesson 802

We've just landed on the very last page of the book — the tail end of the index. This is the part where all the topics we've covered are alphabetically listed with their page numbers, so you can find them again quickly. Let me walk you through the entries we see here, because even an index tells you something about how the book is organized. Starting with W, we have the Wedge Plate on page 155. That's a component in an instrument — I'd expect it to be part of a gyroscopic or pressure-sensing mechanism, but the index just points us to where it's discussed. Next, the White Arc on page 45. That's a marked range on an airspeed indicator — the flap operating range. And right below it, the Yellow Arc on page 45 as well. That's the caution range on the same instrument, the speeds you should avoid except in smooth air. Both are on the same page because they're both markings on the airspeed indicator dial. Then we have Wind Speed and Direction on page 245 — that's the navigation display information, how the wind vector is shown to you. Working Memory on page 309 — that's a human factors term, part of how pilots process information in the cockpit. WXR on pages 282 and 286 — that's the abbreviation for Weather Radar. The X in WXR is the standard aviation shorthand for "weather" — you'll see it in weather radar systems. Moving to X, we have XTK/TKE on page 243. XTK is Cross-Track Error — how far left or right you are from your intended path. TKE is Track Angle Error — the angular difference between your actual track and the desired track. Both are navigation display readouts. Under Y, we have the Yaw Damper on page 403, and Yaw Damper Indications on page 407. The yaw damper is the system that automatically controls rudder movement to stop the aircraft oscillating around the yawing axis — the vertical axis through the aircraft. The indications are what you see on the instrument panel to confirm it's working. And finally, the Yawing Plane on page 153 — that's the plane of motion around the vertical axis, the one the yaw damper controls. So that's the end of the index, and the end of the book. Every one of these entries — the Wedge Plate, the White and Yellow Arcs, Wind Speed and Direction, Working Memory, WXR, XTK/TKE, the Yaw Damper and its indications, and the Yawing Plane — they're all topics we've covered in detail throughout the course. The index is your map back to any of them.