Moving to E — Page 573, Lesson 571

This is the index of the book — the alphabetical list of topics and the page numbers where you'll find them. I want to walk you through the entries that appear here, because each one is a technical term you're going to meet in the chapters ahead, and it helps to have a preview of what they mean before you dive in. Let's start with the D entries. Diurnal — that's page 51 — refers to something that happens on a daily cycle, related to the Earth's rotation. Double Track Angle Error — page 200 — is a navigation error you'll encounter when working with certain types of compass or directional systems. Drift — page 125 — is the angular difference between the heading you're steering and the track you actually make good over the ground, caused by wind. Moving to E. Earth Convergence — page 241 — is the rate at which meridians converge toward the poles, a fundamental concept in map projections. Earth Rate — page 465 — is the angular velocity of the Earth's rotation, which matters for inertial navigation. Equatorial Diameter — page 3 — is simply the diameter of the Earth measured across the equator. European Datum 1950 Model (ED50) — page 3 — is a geodetic reference system, a standard model of the Earth's shape used for mapping and positioning. Under F, we have Fix — page 477 — which is a position determined by navigation observations, and Fixing Position — page 479 — the process of establishing that position. Under G, there's a cluster of related terms. Geodetic Latitude — page 10 — is the angle between the equatorial plane and the normal to the ellipsoid at a point. Geodosy — page 3 — is the science of measuring the Earth's shape and size. Geoid — page 3 — is the equipotential surface of the Earth's gravity field, the shape the oceans would take. Graduated Scale Line — page 223 — is a line on a chart marked with a scale for measuring distances. Graticule — pages 293 and 8 — is the network of meridians and parallels on a chart. Great Circle — page 7 — is the shortest path between two points on a sphere, the intersection of the sphere with a plane through its centre. Great Circle Vertices — page 16 — are the points of maximum latitude on a great circle. Greenwich Anti-meridian — page 13 — is the meridian exactly opposite Greenwich, at 180 degrees. Gridded Charts — page 458 — are charts overlaid with a grid system for polar navigation. Grid Minimum Off-route Altitude (Grid Mora) — page 221 — is a minimum safe altitude expressed relative to the grid. Grid North — page 459 — is the direction of the grid lines on a gridded chart. Grid Ring Compass — page 494 — is a compass with a grid ring for steering by grid directions. Under H, we have Hard Iron Magnetism — page 502 — which is permanent magnetism in the aircraft's structure that affects the compass. Heading — page 62 — is the direction the aircraft's nose is pointing. Horizontality — page 495 — relates to the levelling of an instrument. Hour Angle — page 386 — is the angular distance of a celestial body west of the meridian. Under I, we have Indicated Altitude — page 115 — which is the altitude read directly from the altimeter. Inertial Navigation System — page 45 — is a self-contained navigation system using accelerometers and gyroscopes. Instrument Error — page 105 — is the error inherent in an instrument's readings. So this index is your map of the whole book — every one of these terms is a concept you'll master as we work through the chapters. When you're ready, we'll move on to the next part of the book.