leave the good watch locked up in the camp. In this case, the owner must have a regular time for winding his good watch, say, the last thing before turning in at night, or it may run down and its valued time be lost.

302. Watches may be set at any telegraph office in Luzon at 11 o'clock a. m., Manila time. The signals come at 30-second intervals for several minutes prior to, and at, 11 o'clock. The seconds signals stop just prior to a 30-second or minute period and pick up the new minute or half minute.

303. The daily rate of a good watch can be determined and should be known. It is the amount the watch gains or loses in 24 hours. By comparing the watch for several days, the rate is easily computed. Thereafter, knowing that the watch time was correct on a certain date or that its error was such an amount, its error at any reasonable time thereafter can be computed, provided the watch has been running steadily.

304. To provide for this case, of his watch's stopping, a topographer may observe from his camp the exact watch time of the setting of any bright, easily distinguished star (not a planet). He should record the computed true time. Now, each succeeding night the star will set 3 minutes 56 seconds (approximately) earlier. Therefore, if the watch stops, the topographer will observe from his camp that night, weather permitting, the setting of the star he observed before, and set his watch at the computed time for the star's setting that night.

305. If the horizon is usually hazed over, the passage of the star by any two fixed points may be observed-the eye must be at one point and the star must appear to pass the other point.

306. In case a watch becomes saturated with salt water it should be soaked thoroughly in fresh water, then soaked in oil, and sent to a cleaner.

307. Accurate time on this survey is needed only in the determination of azimuth by direct observations. The methods prescribed are so chosen that the time factor enters the computations, with a minimum value.

SUGGESTIONS TO COMPUTERS.

308. Thorough accuracy is what is demanded in computers. While speed is to be desired, it is always second to accuracy, and computers should continually bear this in mind. They must ac

quire the habit of being sure and accurate. Speed will then come with practice.

309. Field work may be only approximately correct, due to the speed with which it must be taken. The computers, however, must admit of no errors of their own, and must be correct to that degree of precision laid down by these instructions. They should follow these hints closely:

(a) Keep your work neat, systematically arranged. Do not crowd it. Always be able to return to any stop in the computation, finding it in its proper place.

(b) Use the survey forms wherever they are provided and follow them closely. In this way the work becomes more mechanical and chance of error less.

(c) A computer who is inexperienced or out of practice should check his work whenever possible. He should add all columns "up" and "down" before going forward. He should check all subtractions by adding the remainder to the subtrahend. He should check logarithms, either of number or of circular functions, by using first a tabular value less than the given one and then a greater value, so that the differences in one case may be added and in the other case subtracted. This operation may be reversed when the logarithm is given and the number or angle is required.

(d) Many errors are made by taking out the first figures of a logarithm from the wrong line, where a dash over the next figure indicates that the first figures should come from a lower line.

(e) The rules governing the signs of sine and cosine functions should be firmly fixed in the mind. It is well to remember that in the regular conventional plot of the quadrants, with north at the top, all values to the right or up are positive while all others are negative. Until he becomes thoroughly familiar with such signs, the computer should keep a graphical plot of the quadrants before him with the sine and cosine values in each quadrant. For example: Bearing the azimuth Sines positive

1st quadrant

(0°-90°)

N. E.

(f) Check each step in a long computation. If it is not automatically checked, do so by repeating the computation.

(g) Check the copying of angles, distances, etc., taken from note-books or from adjusted results for use in new computations. Check figures carried from page to page.

310. Gross errors are sometimes made by using the sine when a cosine is required or by writing the product in a wrong column, as east for west in a control traverse computation. Placing a decimal point in the wrong place is a common mistake. This may be corrected by a mere inspection of the quantity to see whether it appears of proper value. As logarithms are usually employed in these computations, the correct value of the characteristic should be checked. Remember that the characteristic of the logarithm of a number greater than unity is equal to the number of places, less one, to the left of the decimal, and that the characteristic of the logarithm of a number less than unity is minus and equals the number of zeros plus one between the decimal and the first other figure, or for convenience these minus values are subtracted from 10 and the remainder recorded, as in the circular functions. For example of these "characteristics":

The logarithm of 3000.00-3.47712

311. When computers are duplicating work and a difference is found, each should recompute the result before correcting either, as errors have frequently been made by changing the correct figures.

312. When two persons are comparing a copy with the original, if the reader occasionally calls out a wrong figure or word intentionally and notes whether the error is caught up, it tends to keep the listener more intent on the work.

313. The "Geographic Tables and Formulas," by Gannett, as

I

furnished each field party, contains much data of value to the topographer; that is

Five-place logarithms, pages 127-192;

The A, B, and C functions for positions computation in triangulation, pages 193-267;

Description of the inverse solution, pages 269-270;
Correction for curvature and refraction (C-R) in eleva-
tion computations, page 273;

Logarithmic changes, meters to feet, etc., page 301;
Convenient equivalents, constants, etc., pages 313-315;
The stadia conversion tables on pages 275 and 298 have been
gotten out with the logarithms in this manual (Appendix
"C").

The table of Appendix "C" will be used in computing control traverses, as explained in paragraph 185.

Much data of interest and possible value to the topographer will be found in the front part of Gannett's Tables; for example, the reduction to center, solution of triangles, three-point problem,

etc.

314. Use of the Slide Rule. The slide rule, as issued, can be used to great advantage in checking computations, particularly the latitude and departure components in control traverses. In this work the sine scale on the slide should be numbered inversely in red for the cosine scale. Thus, with a single setting of the slide, both the departure and latitude components may be read off. The 20-inch slide rule should be used for all such work. Complete descriptions for the use of slide rules are usually embodied in a pamphlet sold with the rule. The better texts on surveying explain its use.

MESS AND RATION ACCOUNTS.

315. All survey detachments and parties are subsisted "in the field" upon a special allowance approved by the commanding general.

316. A request for this special allowance, based upon the requirements of previous seasons, upon the probable local conditions to be encountered and upon the present cost of garrison ration, must be made to the commanding general through channels before the parties take the field.

317. The entire command of the topographical inspector is con

sidered as "in the field" for the full period it is in the district assigned.

318. The quartermaster of each district, as supply officer of that command, will keep a separate ration and commissary account with each field party and with the headquarters detachment mess. Each field party and detachment will be required to subsist on its ration allowance. Each officer messing with a detachment or field party will pay to that mess a minimum of the ration allowance for American soldiers. Each quartermaster employee and native laborer will, if not allowed subsistence by regulations, pay the amount corresponding to the ration of his classification-"American" or "native."

319. The chief of party or the commanding officer of the detachment will keep a fund account of his command in the manner prescribed in regulations for company or detachment funds. The savings of these field party funds will be spent for the party mess. Deficits must be met by the chief of party. The final savings of the headquarters detachment mess will revert to the Military Survey Detachment Fund through the quartermaster to the department engineer who is the custodian of the fund.

320. All field party and detachment accounts will be inspected monthly for approval by the topographical inspector. The combined account of the quartermaster will be passed on monthly by the Field Headquarters Council (all the officers on duty there) and approved by the department engineer at such times as he may inspect the account. The quartermaster may requisition through channels to the department engineer for such amounts of the Military Survey Detachment Fund as may be needed for temporary use or to cover extra ration expenses of special expeditions, reconnaissance, etc.

321. At the close of the topographical season all unexpended savings will be taken up by the quartermaster and submitted with his closed account to the department engineer.

Clothing Requisition.

322. Clothing requisition slips should be prepared at field headquarters and issued through the chiefs of party to the men. In the general case, two consolidated requisitions will be sufficient for each season, one in the middle of the period and one at the close. This should provide each man with proper uniform in which to return to his command.