Freedom From Calculation

Every time a ship’s course is laid or changed, or its po­si­tion noted, the nav­i­ga­tor must make and apply cal­cu­la­tions to cor­rect the er­rors caused by var­i­a­tion of the earth’s mag­netic fields, and dev­i­a­tion due to local con­di­tions about the ship. Mis­takes are fre­quent­ly made in ap­ply­ing the cor­rec­tion fac­tors by ap­ply­ing them to the wrong side. An er­ror is thus in­tro­duced, which in mag­ni­tude is twice the cor­rec­tion factor. Ins­tances are re­port­ed of ships being 200 miles out of their courses as a result.

The Gyro-Compass re­quires no cor­rec­tions since it is un­dis­turbed by var­i­a­tions or any local mag­ne­tic con­di­tions. The read­ing in­di­ca­ted by the Sper­ry Gyro-Com­pass is not ap­prox­i­mate—it is ab­so­lute­ly and im­me­diate­ly cor­rect. It is not ne­ces­sary to cor­rect the course every few hours for var­ia­tion—the nav­i­ga­tor is freed from the ne­ces­si­ty of ma­king cal­cu­la­tions.