Gyro magnetic compasses are subject to a large number of errors, some of which may be eliminated, or at least greatly reduced, by careful design on the part of the instrument manufacturer and an intelligent operating drill on the part of the user. Table I shows errors under five basic headings, and allots to each error a symbol classifying it as:

(a) The responsibility of the instrument manufacturer (I)

(b) The responsibility of the aircraft manufacturer or its operator (A)

(c) Inadequate knowledge of the geomagnetic structure of the Earth's field (K)

Some sources of error in Table I are marked with an asterisk. It is these which the designers of the compass system described have endeavoured to eliminate.