Figure 13-12.-Sample field notes from a deflection angle transit-tape survey.2. Read the vernier with the eye directly overthe top of the coinciding graduations to eliminatethe effects of parallax.3. Take the reading of the other vernier as acheck. The readings should be 180° apart.4. Check the plate bubbles before measuringan angle to see if they are centered, but do notdisturb the leveling screws between the initial andfinal settings of the line of sight. If an angle ismeasured again, the plate may be releveled aftereach reading before sighting again on the startingpoint.5. Make sure that the rodman is holding therange pole truly vertical when you sight at it.When the bottom of the range pole is not visible,let the rodman use a plumb bob.6. Avoid accidental movement of the horizon-tal circle; for instance, moving the wrong clampor tangent screw. If a number of angles will beobserved from one setup without moving thehorizontal circle, you should sight at some clearlydefined distant object that will serve as a referencemark and take note of the angle. Occasionally,you should recheck the reading to this pointduring measurement to see if there is anyaccidental movement.An example of a horizontal deflection anglemeasurement is shown in figure 13-12. The fieldnotes contain data taken from a loop traverseshown in the sketch. The transit was first set upat station A, and the magnetic bearing of AB wasread on the compass. Then the deflection anglebetween the extension of EA and AB was turnedin the following manner:1. The instrumentman released both clamps,matched the vernier to zero by hand, tightenedthe upper motion clamp, and set the zero exactlywith the upper tangent screw.2. With the telescope plunged (invertedposition), the instrumentman sighted the rangepole held on station E. Then he tightened thelower motion clamp and manipulated the lowermotion tangent screw to bring the vertical crosshair to exact alignment with the range pole.3. The instrumentman replunged the telescopeand trained on the extension of EA. (Notice thatthe telescope is in its normal position now.) Hethen released the upper motion and rotated thetelescope to the right until the vertical cross haircame into line with the range pole held onstation B. He further set the upper motion clampscrew and brought the vertical cross hair intoexact alignment with the range pole by manipu-lating the upper motion tangent screw.4. The instrumentman then read the size ofthe deflection angle on the A vernier (89°01´).Since the angle was turned to the right, herecorded 89°01´R in the column headed “Defl.Angle.”Likewise, he recorded the chaineddistance between stations A and B and themagnetic bearing of traverse line AB under theirappropriate headings.13-11
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