Planetable and Telescopic Alidade
Adjustments of the telescopic alidade require no principles of adjustment other than those for the transit or level. Survey work done with the planetable and the telescopic alidade need not be as precise as that done with the transit, so the adjustments are not as refined.
Because the telescope is not reversed in a vertical arc, no appreciable error is caused because the line of sight is not perpendicular to the horizontal axis, or the line of sight is not parallel to the edge of the ruler. It can also be assumed without appreciable error that the edges of the ruler are straight and parallel and that the horizontal axis is parallel to
the surface of' the ruler.
Adjust the control level so that its axis is parallel to the ruler. The test and correction are the same as described for adjustment of the plate levels of the transit except that the plate or ruler is reversed by carefully marking a guideline on a planetable sheet. The board is not reversed. Adjust the vertical crosshair so that it lies in a plane perpendicular to the horizontal axis. The test and adjustment are the same as for the transit.
Adjust the telescope level so that its axis is parallel to the line of sight. The test and correction are the same as described f or adjustment of' the telescope level on the transit.
If the alidade is one in which the telescope can be rotated about its axis in a sleeve. the two following adjustments should be used. First make the line of' sight coincide with the
axis of the telescope sleeve. In making the test, sight the intersection of the crosshairs on some well-defined point and rotate the telescope carefully through 180". Generally, the rotation is limited by shoulder and lug. If the intersection of the crosshairs stays on the point, the line of sight coincides with the axis of the telescope sleeve.
Second, make the axis of the striding level parallel to the telescope sleeve and therefore
parallel to the line of sight. In making the test, place the striding level on the telescope and bring the bubble to the center of the level tube. Then carefully remove the striding level, turn it end for end, and replace it on the telescope barrel. If the bubble returns to the center of the tube, the level is in adjustment. If the bubble is not centered, it should be brought back one-half of the displacement by means of the adjusting screw on one end of the
bubble tube. Then bring the bubble to the center by means of the tangent screw and repeat the test. Adjust the vernier to read zero when the line of sight is horizontal. This adjustment is the same as described for the transit under "Adjustment of 'I'elescope Bubble."
Lesson 14
Hand Signals Survey
Agood system of hand signals between members of a surveying party is a more efficient means of communication than is possible by word of mouth.
Any code of signals mutually understood by the persons handling the instrument and the rod is good if it works. When the "shot" is finished, prompt signalling by the instrument handler allows the rod holder to move promptly to the next point. It is also desirable to have a system of signaling so that numbers can be transmitted from rod holder to instrument handler or vice versa.
The code of signals illustrated in figures 1-16 and 1-17 is suggested. This code may be enlarged upon oraltered to suit the needs of the job. Adefinite code, however, should be determined and mutually understood in order to speed up the job.
Notes and Symbols
Field notes are the record of a survey, with data recorded so that they can be interpreted readily by anyone having knowledge of surveying. Notes should identify the survey by title and should include location and purpose, identification of survey party members and duties, date, and weather conditions. Notes should be recorded in the field notebook at the time work is done and not left to memory or later recopied from temporary notes. All
data pertaining to one survey or project should be entered in the same field book or series of field books. Books should be identified and indexed according to SCS standard notekeeping procedures before notes are recorded. (Refer to TR-62.)
Notes consist of numerical data, explanatory statements, and sketches. The form in which notes are recorded varies with the kind of survey, such as bench level circuits, profiles and cross sections, transit-traverses, etc. However, a uniform system for each kind should be followed insofar as possible. Sample forms of field notes are illustrated throughout
this chapter and in TR-62. Sketches in field notes are important in conveying
information and correct impressions to others plotting data or using the information in engineering design. Sketches should be drawn approximately to scale, using standard SCS mapping symbols. Some of the more commonly used symbols are shown in figures 1-18 and 1-19. 
Lesson 15