This method gives an exact result. By converting theminutes to a decimal part of a degree to the nearest fivesplaces, you obtain the same result.Simple Curve LayoutTo lay out the simple curve (arc definition) justcomputed above, you should usually use theprocedure that follows.1. With the instrument placed at the PI, theinstrumentman sights on the preceding PI or at a distantstation and keeps the chainman on the line while thetangent distance is measured to locate the PC. After thePC has been staked out, the instrumentman then trainsthe instrument on the forward PI to locate the PT.2. The instrumentman then sets up at the PC andmeasures the angle from the PI to the PT. This angleshould be equal to one half of the I angle; if it is not,either the PC or the PT has been located in the wrongposition.3. With the first deflection angle (3°10’) set on theas the first subchord distance (42.18 feet) is measuredfrom the PC.4. Without touching the lower motion screw, theinstrumentman sets the second deflection angle (6°55’)on the plates. The chainman measures the chord fromthe previous station while the instrumentman keeps thehead chainman on line.5. The crew stakes out the succeeding stations inthe same manner. If the work is done correctly, the lastdeflection angle will point on the PT. That distance willbe the subchord length (7.79 feet) from the last stationbefore the PT.When it is impossible to stake out the entire curvefrom the PC, a modified method of the proceduredescribed above is used. Stake out the curve as far aspossible from the PC. If a station cannot be seen fromthe PC for some reason, move the transit forward andset up over a station along the curve. Pick a station fora backsight and set the deflection angle for that stationon the plates. Sight on this station with the telescopeplates, the instrumentman keeps the chainman on linein the reverse position. Plunge the telescope and setFigure 11-11.—Inaccessible PI.11-10
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