First, a quick note on the range — Page 297, Lesson 352

Right, let's pick this up with the MAP display on the Electronic Flight Information System, or EFIS. This is the mode you'll use most in normal operations, so let's get the details right. First, a quick note on the range. On the control panel you select the range of the display. The display itself shows the half-scale range. So if you see "10 NM" displayed, that's the half-scale value, meaning the display is actually selected to 20 NM. The outer arc of the compass rose represents the furthest range from the aircraft — that's your 20 NM edge. Now, the MAP mode itself. This is the normal mode. It works in conjunction with the flight plan data programmed into the flight management computer, the FMC. The FMC feeds the display, and the display shows information against a moving map background. All the elements on that map are drawn to a common scale, so everything is consistent. Look at the layout. The symbol representing the aircraft sits at the lower part of the display. At the upper part, you have an arc of the compass scale, or compass rose. That arc covers 45 degrees on either side of the instantaneous track. So you see a 90-degree arc total, centered on where you're heading right now. Heading information comes from the appropriate inertial reference system, the IRS. The compass rose is automatically referenced to magnetic north when you're between latitudes 73°N and 65°S. That's the normal case. There's a crew-operated MAG/TRUE selector switch. When you're above those latitudes — north of 73°N or south of 65°S — the rose automatically references to true north instead. And if you manually set the selector switch to TRUE, the compass rose is referenced to true north regardless of latitude. Now the route display. The aircraft's active route, as derived from the FMC, is shown as a magenta coloured line joining the waypoints. The active waypoint — the one you're currently navigating towards — is shown as a magenta coloured star. The other waypoints on the active route are called inactive waypoints, and they're shown as white stars. Both types are identified by name. At the top of the display, you'll see the distance to the next waypoint and the time at the next waypoint. Weather radar returns, the WXR data, and range arcs are displayed when the WXR switch is on. There may also be a turbulence mode, shown as +T, which works as previously described. Other data is also displayed: wind speed and direction, and lateral and vertical deviations from the selected flight path. Here's a clever part. The FMC can predict events. It combines current ground speed and lateral acceleration to show either a curved trend vector, which is white, during turns — or a range to altitude arc, which is green, during climb or descent. Off-route waypoints, airports, and nav aids can all be shown in their relative position to the aircraft's progress and the selected range. And you can select additional waypoint information to be displayed, like altitude and time. So to tie it together: the MAP display gives you a moving map, aircraft symbol at the bottom, a 90-degree compass arc at the top, magnetic or true reference depending on latitude and the MAG/TRUE switch, magenta for the active route and active waypoint, white for inactive waypoints, and predictive trend vectors in white or green. That's the core of what you'll see on the EHSI in MAP mode.