Page 15 peeliminary 124 



124. Units of Measurement 



The following units of measurement, with fractional parts in decimals of the same 

 unit, shall be used in surveys, reports, and statistics of the Coast and Geodetic Survey: 



(a) Depth of the water — in fathoms, or feet. (For smooth-sheet plotting, see 7711 and 

 7712.) 



(6) Measured horizontal distances on land or in the water, and short estimated horizontal dis- 

 tances over the water — in meters. 



(c) Long estimated distances over the water and ship's run distances — in nautical miles. 



(d) Elevations above the topographic datum plane or above the sounding datum — in feet. 



(e) Subaqueous distances — in seconds of time (at a given velocity of sound), or meters. 



(/) Statistics of horizontal distances, except for ship's run (see (c) above) — in statute miles. 

 (g) Statistics of surveyed areas, either water or land — in square statute miles. 

 (h) Current velocity and speed of vessel — in knots. 



(z) Bearings from zero at true north clockwise through 360° — in degrees. (Not to be confused 

 with geodetic azimuths, which are reckoned from zero at true south.) 



It is to be noted that the short distances estimated during a hydrographic survey 

 and entered in the Sounding Record shall be in meters. This pertains to the estimated 

 distance of the sounding boat or launch from the high-water line or the estimated dis- 

 tance the sounding vessel passes abeam of any object, danger, or aid to navigation. 



125. Confidential Surveys 



Surveys of a confideixtial nature are occasionally made by the Bureau and the 

 results of surveys of certain areas are at times made confidential at the request of one 

 of the Military Services. Special instructions, stating the precautions to be taken, 

 will be issued whenever confidential field operations are to be executed. 



Such surveys are classified and marked as confidential when they are registered, 

 and no copies of these shall be furnished to the public. Photographic copies of con- 

 fidential surveys will be furnished to field parties who have need for them in connection 

 with their survey operations. Each Chief of Party is responsible for those forwarded 

 to him, although when necessary he may permit their use by responsible assistants. 

 These photographic copies are always plainly marked "confidential" and they must 

 be returned to the Washington Office for disposal, after the operations have been 

 completed. (See also 1321.) 



Whenever any confidential matter is forwarded through the mails it shall first 

 be enclosed in a package marked CONFIDENTIAL and addressed personally by name 

 to the person who is to be responsible for its custody. This envelope or wrapped 

 parcel is then enclosed in an outer wrapping and addressed to that person in the usual 

 manner for official mail. The outer wrapping must contain no reference whatsoever 

 to the confidential nature of the contents. Such material must always be sent by 

 registered mail. 



13. PROJECT PLANNING 



131. Data From Prior Surveys 



Copies of all prior survey data that are considered necessary in connection with 

 the combined operations of the project will be furnished with the project instructions. 

 Photostat, lithographic, or blueprint copies of the control data — geographic positions, 

 descriptions, and triangulation sketches — will be furnished when these have not been 

 published in the geodetic publications. Copies of all topographic and hydrographic 



