The directional system mounting in the compass bowl shall be constructed in such a way that it returns to the original position on its pivot when the bowl is inverted and then returned to its normal position.

　

This can be checked by inspection.

　

The directional system and the compass bowl shall be constructed in such a way that the directional system can rotate freely when the compass bowl is tilted in any direction at an angle of:

　

a)	10°when the compass bowl has an external gimbal system;

　

　

The examination may be carried out by means of a revolving platform with adjustable inclination.

　

　

Each compass shall be fitted with a lubber mark indicating the direction of the ship's head (main lubber mark). This main lubber mark shall be clearly identifiable and be within 0,5°of the fore and aft gimbal axis.

　

Other lubber marks are allowed, showing the direction of the ship's stem and thwartship respectively. These lubber marks shall fulfill the conditions laid down in 4.2.2.5.2 to 4.2.2.5.4.

　

The main lubber mark shall be of such design that the card may be read from the steering position against the lubber mark when the compass bowl is tilted as in 2.2.4.3. In the case of a gimbaled compass, the use of a plate lubber line is permitted (see also 2.2.6.1.2).

　

The examination may be carried out by visual inspection in conjunction with the examination in 2.2.4.3.

　

The width of the lubber mark(s) shall not subtend an angle greater than 0,5°of the card graduation.

　

The examination may be carried out by visual inspection.

　

The distance between the lubber mark(s) and the card outer edge shall be between 1,5 mm and 3 mm except in the case of projector compasses, when the tolerance shall be between 0,5 mm and 1,5 mm.

　

The examination may be carried out by using a mirror gauge which is laid on top of the bowl rim, or by travelling microscope, or by direct measurement when the compass is dismantled.

　

In the case of hemispherical compasses, this becomes a type-test only and can be ascertained when the compass is dismantled.

　

　

　

　

The compass card shall be graduated in equal interval of the values in the following table, starting from North in the clockwise direction as viewed from above. Each tenth degree should be marked with the three corresponding numbers. North should also be indicated by 000°. The cardinal points shall be indicated by the capital letters N, S, E and W; the intermediate points may also be marked.

Alternatively, the North point may be indicated by a suitable symbol.

The card shall be numbered every angle in the following table.

　

　

Where the compass card is printed on both sides, the graduations shall coincide with a tolerance of 0,2°.

　

The examination shall be carried out visually.

　

The diameter of the compass card for binnacles of the following types are as the following tables:

　

　

Steering compass shall be possible for a person with normal vision to read at a distance with the class of magnetic compasses an the following table, in both daylight and artificial light, those graduations on the card which are contained within a sector whose width is not less than 15° to each side of the lubber mark. The use of a magnifying glass is permitted.

For reflecting and projecting compasses, the lubber mark shall be visible and the 30°sector of the card shall be readable by a person with normal vision at a distance of 1 m from the periscope tube.

　

　

The use of a magnifying device is permitted.

　

The examination shall be carried out visually.

　

　

The magnetic moment of the directional system shall, depending on the card diameter, be not less than the values given in figure 1.

　

Testing may be carried out by means of a magnetometer (deflection method) or any other appropriate means.

　

　

To avoid the induction error which is caused by an inadequate arrangement of magnetic elements in the directional system and introduced by magnetic induction in correctors (iron spheres or similar conventional correctors) of coefficient D due to the magnetic elements in the directional system, one of the following requirements shall be fulfilled:

　

a) The poles of the directional system magnets shall be arranged in such a way that no excess sextantal or octantal deviations will be produced by the influence of the correcting devices. The criterion for this is the ratio of octantal and quadrantal coefficients H/D, and the ratio H/D shall not exceed 0,08. (ISO 2269, 2.2.6.2.2)

　

The test shall be carried by the four corrector method of Meldau, or any other equivalent method.

　

In the Meldau test, the compass shall be mounted on a stand and two soft iron correctors placed diametrically opposite and symmetrical to the rotation centre. The device with the two soft iron correctors shall then be rotated around the fixed compass and coefficient D calculated.

　

To cancel out the quadrantal deviation, two additional exactly similar correctors shall be placed at the same distance from the centre with their line of connection at right angles to that of the original pair.

　

The arrangement of the four soft iron correctors shall then be rotated around the compass and coefficient H calculated.

　

From these values the ratio of the coefficient H to coefficient D is obtained.

　

b) The coefficient E of the sextantal deviation caused by a small magnet, less than 50 mm in length, placed in the same horizontal plane as the magnetic elements at a tangential distance of about 40 cm from the centre of the directional system, is less than 0,01 of coefficient B of the semicircular deviation.

　

4.2.2.6.2.3 Change in tilt when vertical flux density has changed (type-test only)

The tilt of the directional system card when balanced and assembled in the bowl shall not exceed: 0,5°in the E-W direction and (0,5 ±0,03 σ)°in the N-S direction, σ being the absolute value of the algebraic difference between the values of the vertical magnetic flux density in microteslas at one location and at any other location.

　

The test shall be carried out with liquid-filled compasses of the conventional type when the bowl is dismantled or by means of a suitable optical device when closed. In the case of other compasses, the test may be carried out when the bowl is dismantled.

　

　

Following an initial deflection of the card of 90°from the magnetic meridian, the time taken to return finally to within 1°of the magnetic meridian, shall not exceed 240/√H at a temperature of 20℃ ±3℃, where H is the horizontal component of the magnetic flux density in microteslas (μT) at the place of testing.

　

This is repeated on the other side of the meridian and the mean is taken.

　

　

The directional error is a directional system constructional error. it is composed of

　

　

　

　

The directional error shall on no heading exceed the values in the following table.

　

　

The examination may be carried out on a compass test stand. After having brought the rotation centre of the compass card into the rotation axis of the test stand, the directional error can be read at the card graduation by means of a telescope or any other appropriate means, when the vertical plane of the sight passing through the rotation axis has been aligned with the magnetic meridian in advance. This measurement shall be carried out on at least four equidistant headings. When measuring, the top glass shall be tapped gently to eliminate the error due to friction (see 2.2.7.3).

　

In transmitting compasses, the directional error applies to the compass without fluxgate. The fluxgate of a transmitting compass shall be placed so that the influence on the card heading shall not exceed the values in the following table on any heading.

　

　

　

Lubber error is a constructional error of the compass bowl and gimbal, which depends on the relative position of the main lubber mark (if it is fixed), the pivot bearing, and the direction of the outer gimbal axis.

　

For compasses with a movable lubber mark, but with an auxiliary graduation for coefficient A correction, also in transmitting compasses or compasses which operate auto-pilots with a rotatable compass bowl, the lubber mark shall be brought into the zero position before testing.

　

No lubber error shall exceed the values in the following table.

　

　

For compasses with a movable lubber mark, but without an auxiliary graduation or other means of securing a definite position of the lubber mark in relation to the direction of the outer gimbal axis, or for compasses without gimbals, as in hemispherical compasses for steering purposes only, the lubber error becomes undefined and cannot be determined.

　

The examination may be carried out on a compass test stand by bringing the outer gimbal axis into the vertical plane of view passing through the rotation centre of the test stand and reading the master graduation vernier. After this the pivot point shall be brought into the rotation centre of the test stand and the compass support turned until the lubber mark lies in the vertical plane of view.

　

The angle of rotation is the lubber error.