The Lambert's arithmetic
Every Lambert calculation is one fact wearing four hats; a straight line's direction changes across the sheet by the chart convergence, Δlong × n:
the track change — a straight line crossing 16° of longitude on a chart with n = 0.75 changes direction by 16 × 0.75, which is 12°.
initial, final and rhumb-line tracks — the final track is the initial plus the convergence (eastbound in the north), and the rhumb-line track is their mean, the initial plus half: leaving on a straight-line track of 072 across 20° of longitude with n = 0.6 (convergence 12°), the arrival track is 084 and the rhumb-line track 078.
the parallel of origin from a measured convergence — run backwards: n = convergence / Δlong, and the parallel of origin is the angle whose sine that is: 15° of convergence over 20° of longitude gives n = 0.75, a parallel of origin of about 48.6°N. The same division answers the chart-in-hand question, since a Lambert chart's constant of the cone can be determined by measuring the angle between two meridians and dividing by their change of longitude (or simply read from the chart's title block).
the change of longitude from two straight-line tracks — Δlong = (final track − initial track) / n: tracks of 070 at one position and 082 at another on an n = 0.8 chart lie 12/0.8, which is 15° of longitude apart.
Symbols on the sheet
ICAO Annex 4 standardises the chart's vocabulary so that any crew can read any sheet, and recognising the standard symbology is a stated objective. The working core:
aerodromes — circles (with runway layouts inside at larger scales);
obstacles — pointed symbols, marked with light-flash rays when lit and doubled for a group;
restricted, prohibited and danger areas — outlined and labelled R, P and D with a number;
radio aids — by shape, the compass rose of the VOR (VHF omnidirectional radio range), the dotted disc of the NDB (non-directional radio beacon);
isogonals — dashed lines carrying their variation value, the vocabulary of the first lesson printed on every sheet.
Working the chart
Measurement on the Lambert respects its convergence: a track is measured against the meridian nearest the mid-point of the leg, because the end meridians point differently, and the mid-meridian's answer is the rhumb-line average the flight will hold. Distance is taken from the latitude scale at the leg's mean latitude, one minute of latitude being one nautical mile, and never from the longitude scale, whose minutes shrink with the cosine of latitude.
The radio aids turn chart work into fixing. A VOR radial and a DME (distance-measuring equipment) range from a co-located station cross in a fix: the radial, a magnetic bearing from the station, is converted to true with the variation at the station, plotted outward from it, and cut with the DME arc. The NDB asks one sum first: the relative bearing read from the ADF (automatic direction-finding equipment) is added to the true heading to give the true bearing to the beacon, and the reciprocal is plotted from it: heading 060 true with the needle showing a relative bearing of 090 puts the beacon on a true bearing of 150, so the position line leaves the beacon on 330. Because the ADF measures at the aircraft, any magnetic conversion uses the variation at the aircraft, where the VOR's radial, measured at the station, used the station's: the small print that separates the two aids in the exam.