Look at the entries here — Page 573, Lesson 575

This is the index of the General Navigation book — the alphabetical list of topics with their page numbers. I want to walk you through what this index tells you about the structure of the course, because it's actually a roadmap of everything we're going to cover together. Look at the entries here. Under P, we have Pressure Altitude on page 88, and Pressure (or Position) Error on page 105. These are two different concepts. Pressure Altitude is the altitude indicated when you set your altimeter to the standard pressure setting of 1013.25 hectopascals — it's the height above the standard datum plane. Pressure Error, also called Position Error, is something else entirely: it's the error in your airspeed and altimeter readings caused by the position of the static vents on the aircraft, where the airflow around the fuselage disturbs the pressure being sensed. Two distinct ideas, both under P. Then under Q, we have the radio bearing terms: QDM on page 478, QDR on page 478, and QTE on page 478. These are the Q-codes used in VHF direction finding. QDM is the magnetic bearing from the aircraft to the station — the heading you'd steer to fly directly to the beacon. QDR is the magnetic bearing from the station to the aircraft — the reciprocal. QTE is the true bearing from the station to the aircraft, measured from true north rather than magnetic north. All three on the same page because they're taught together as a set. Also under Q, we have Quadrantal Directions on page 4. That's the system of naming directions by quadrant — north-east, south-west, and so on — rather than by degrees from north. Under R, we have Rate of Descent on page 212, which is simply the vertical speed at which the aircraft descends, usually expressed in feet per minute. Then Real Variation Map on page 48 — that's a chart that shows the actual magnetic variation across the Earth's surface at a given epoch. Reciprocal Directions on page 6 — that's the opposite direction, 180 degrees from a given heading. Rectified Airspeed, abbreviated RAS, on page 105 — that's your calibrated airspeed corrected for position error, the speed you read on the airspeed indicator after accounting for the static vent error I mentioned a moment ago. And Relative Bearing on page 481 — the angle measured clockwise from the aircraft's nose to the direction of a station or object. Then Resolution Accuracy on page 14 — that's about how precisely a navigation system can resolve or display a position. Returning to Track on page 199 — the technique of getting back onto your planned route after being blown off it by wind. And Rhumb Line on page 24 — a line that crosses all meridians at the same angle, so it appears as a straight line on a Mercator chart but is actually a spiral on the globe. Under S, we have Scale on pages 223 and 275 — the ratio between distance on the chart and distance on the ground. Secant on page 296 — a mathematical function used in map projections where a cone or cylinder cuts through the Earth's surface. Secular on page 51 — that's the long-term, gradual change in magnetic variation over many years, as opposed to short-term changes. Sensitivity on page 495 — how responsive an instrument or system is to a change in input. Sexagesimal System on page 5 — that's our base-60 system of measuring angles and time, where one degree has 60 minutes and one minute has 60 seconds. Sidereal Day on page 384 — that's the time it takes the Earth to rotate once relative to the fixed stars, about 23 hours 56 minutes, as opposed to the solar day. Small Circle on page 8 — any circle on the Earth's surface that is not a great circle, so its plane does not pass through the Earth's centre. Soft Iron Magnetism on page 502 — magnetism induced in soft iron components of the aircraft by the Earth's magnetic field, which affects the compass. Solar Activity on page 51 — variations in the Sun's output that affect the Earth's magnetic field and thus magnetic variation. Speed on a Glide Slope on page 213 — the airspeed you maintain while flying down the instrument landing system glide slope. Spot Elevations on page 221 — the exact heights marked at specific points on a chart, usually in feet or metres. Standard Grid on page 458 — a grid system applied to a chart for navigation, where the grid lines are aligned to a reference direction rather than true north. Standard Nautical Mile on page 30 — the international nautical mile of 1852 metres, the unit we use for distance in navigation. Standard Parallels on page 340 — the lines of latitude where a conic projection is true to scale, where the cone cuts the Earth. Standard Polar Grid on page 466 — the grid system used for navigation in polar regions where meridians converge so rapidly that a special grid is needed. And finally Standard Time on page 401 — the local time adopted by a country or region, based on a whole number of hours from Greenwich Mean Time. So this index is your map of the whole course. It shows you the building blocks — starting with basic direction and the sexagesimal system, moving through charts and projections, then into navigation techniques, and finally into the instruments and radio aids. Every one of these terms we will meet properly in its own chapter. For now, just recognise the shape of it: the fundamentals of direction and distance come first, then the Earth and its magnetism, then charts, then the practical art of navigating, and finally the instruments and radio systems that do the work for you.