Provisional drill and service regulations for field artillery (horse and light) 1916 ... by United States. War Dept

Author:United States. War Dept
Language: eng
Format: epub
Publisher: Govt. print. off.

Measurement of Angles.

1177. Angles may be measured in mils by means of the telescope, the aiming circle, the ruler, the scale in the field glass or its known field of view, or by handbreadths.

The telescope and the aiming circle are instruments of precision. The graduated field glass affords means of measuring angles accurately. When neither the telescope nor aiming circle is available, or when time does not admit of their being set up, use may be made of the less reliable means, practice with which will insure considerable accuracy.

1178. For preliminary practice, horizontal and vertical scales of mils should be laid off on any convenient vertical surface, using an instrument of precision.

As the ruler is already graduated the distance at which it should be held from the eye so that its graduations will cover corresponding spaces on the scales must be determined by trial. Usually this distance is then fixed by tying the ruler cord to the clothing or by knotting it anil holding the knot In the teeth.

When the hand is used for angular measurements, its distance from the eye should be such as may be assumed naturally and uniformly and maintained without fatigue. The portions of the scales then covered by different parts of the hand can be determined and memorized.

The width of the field of view of the field glass can be determined similarly and quite accurately divided by eye into halves, quarters, and eighths.

In making the above calibrations the operator must stand at the position of the instrument used in establishing the scales.

1179. For measuring by handbreadths, each individual will obtain the best results by predetermining, according to the methods just described, the value in mils of certain parts of the hand.

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