2736

THE NEW ZEALAND GAZETTE.

[No. 77

Magnetic bearing.

38. No magnetic bearings are admissible unless for filling in topographical detail work, and then very sparingly, and with permission only.

Offsets.

39. Offsets to irregular boundaries such as rivers, streams, terraces, and fences must not exceed 2 chains in length, and must be taken at intervals in the traverse not greater than 3 chains, but at shorter distances when necessary to correctly define the irregularities of such boundaries.

Astronomical check.

40. In case of long traverses in the bush where check bearings cannot be obtained, recourse should be had to stellar or solar observations for checking bearings, such observations being duly noted in field-book and referred to on plan.

Recording observations.

41. Trigonometrical observations and connections must be given in detail on the proper forms, and the astronomical observations and the results derived therefrom must also be entered on the forms and forwarded with the plan.

Road-traverse.

42. After being graded and located the road-lines should be traversed along the centre, the traverse stations being selected on the line of the grade as nearly as may be.

River-bed traverses.

43. In cases where traverses are carried along or through an open river-bed, and the stations are not on safe ground, it will be necessary, at intervals of not more than 20 chains, to place reference pegs or iron tubes properly connected with the traverse in secure positions on the banks, and record their positions in field-books and on plans. This also applies specially to dredging claims.

Hanging traverses.

44. Where surveys are not closed on trig. stations or by circuit traverse, all “hanging” lines must be twice measured and observed, and a note to this effect must be recorded on plan and in field-book.

Close on to former surveys.

45. The connection and close with former surveys must be clearly shown. Should “adopted” work fail to close with the new work within the prescribed limits, a resurvey of the old work must be made.

Adopted work.

46. The Chief Surveyor, before permitting old work to be “adopted,” may, in his discretion, require it to be verified or resurveyed.

Features to be shown.

47. Notes are to be made of all crossings of creeks and tracks in public use; also such other notes as will enable the topographical features to be delineated on the working-plan, together with buildings and boundary-fences.

Limits and elimination of error.

48. The error attached to the traverse survey necessarily varies with the nature of the ground, and should not be allowed to accumulate above 10 links. Where the accumulation exceeds this amount it will be necessary to have recourse to subsidiary triangulation to correct or reduce the error. On an average, surveyors can measure a mile within an error of 2 links; the limit of error in traverse must in no case exceed 4 links to the mile. Should the error in closing with the triangulation, or other recognised established point, exceed this limit, the work must be revised. So also traverses should close in bearing with an error not exceeding 2' of arc. The difference or error of closure within these limits is to be eliminated by distribution in the usual manner in proportion to the length of the whole traverse to that of each line.

Reduction of traverses.

49. All traverses executed by the surveyor are to be computed and co-ordinated in terms of the meridian and perpendicular of the initial station. These computations must be kept worked up to