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Kurs gjældende Værdi af Compassets Deviation corrigeredes
den i Grader udtrykte observerede Vindretning til den
rigtige misvisende.

Med disse Data udførtes Beregningen af den sande
Vindhastighed og den misvisende virkelige Vindretning paa
følgende grafiske Maade.

Paa "Kobbel-Rosenaf hvilken Fig. 9 viser dot
centrale Parti gjengivet, kun med Udeladelse af de i
Originalen optrukne Streger for hver enkelt Grad udenfor Af-

standen 5, lagdes et Stykke Kalkerpapir. Centrum af Rosen
afmerkedes paa dette, og Nord-Syd-Linien blev optrukket.
Det bidrager til Nøjagtighed at optrække ogsaa
Øst-Vest-Linien gjennem Centrum. Fra Centrum afsattes 1) Skibets
(misvisende) Kurs og Fart, og Endepunktet paa denne
Linie merkedes; 2) den observerede Vinds (misvisende)
Retning og Hastighed, og Endepunktet merkedes.
Kalkerpapiret flyttedes nu saaledes, at det første Punkt faldt i
Rosens Centrum, og de optrukne Nord-Syd- og
Øst-Vest-Linier orienteredes parallel med Rosens tilsvarende
verti-cale og horizontale Linier. Punktet No. 2 angiver da den
virkelige (misvisende) Vindretning og Hastighed.

Ved Hjelp af Misvisningen reduceredes den saaledes
fundne, i hele Gader udtrykte, misvisende Vindretning til
sand Vindretning.

Den geometriske Construction kunde naturligvis
udføres med de retvisende Kurser og Vindretninger eller med
de observerede, i hvilket sidste Tilfælde man til Slutning
havde at anbringe den totale Compas-Fejl som Correction.

deviation of the compass found for the course of the vessel
(ship’s head by C.), the observed direction of the wind,
expressed in degrees, was corrected to the true magnetic course.

Fig. 9.

With these data, the computation of the true velocity
of the wind and the true magnetic direction of the wind
was made diagrammatically, as follows: —

On the Course mid Distance Card, of which the central
portion is represented in Fig. 9, with the omission only of
the radial lines drawn for each separate degree beyond

the distance 5, was laid a piece of transparent paper. The
centre of the card was marked on this paper, and the
North-South diameter-line drawn. Additional accuracy
is secured by also drawing the East-West diameter-line.
From the centre was laid off 1) the ship’s magnetic course
and speed, the terminal point of this line being marked;
2) the magnetic direction and velocity of the observed wind,
the terminal point of the line being marked. The
transparent paper was now moved so that the point first marked
was made to coincide with the centre of the card, and the
North-South and East-West lines were parallel with the
vertical and horizontal lines of the card. Point 2 would then
indicate the true (magnetic) direction and the velocity of
the wind.

By means of the variation, the magnetic direction of
the wind, thus found and expressed in whole degrees, was
reduced to the true direction.

The geometrical construction could of course be made
with the true courses and directions of the wind, or with
those observed; in the latter case, the total compass-error
had to be applied as a correction. I preferred the method

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