Chord Corrections

Frequently, the surveyor must lay out curves more precisely than is possible by using the chord lengths previously described.

To eliminate the discrepancy between chord and arc lengths, the chords must be corrected using the values taken from the nomography in table A-11. This gives the corrections to be applied if the curve was computed by the arc definition.

Table A-10 gives the corrections to beapplied if the curve was computed by the chord definition. The surveyor should recall that the length of a curve computed by the chord definition was the length along the chords. Figure 5 illustrates the example given in table A-9. The chord distance from station 18+00 to station 19+00 is 100 feet. The nominal length of the subchords is 50 feet. Tables A-9, A-10 and A-11 from FM 5-233, are available on the PDH website.