Practice Question: Back-Calculate Benchmark Elevation from Survey Data

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Solution

Answer: C) 114.8 ft

Determine Height of Instrument (HI) between TP 1 and TP 2:
\[HI_2=TP_2+FS_2\]
\[HI_2=120.4 \ ft+1.8 \ ft=122.2 \ ft\]
Determine elevation at TP 1:
\[TP_1=HI_2-BS_2\]
\[TP_1=122.2 \ ft-5.1 \ ft\]
\[TP_1=117.1 \ ft\]
Determine elevation at Height of Instrument (HI) between TP 1 and BM:
\[HI_1=TP_1+FS_1\]
\[HI_1=117.1 \ ft+2.3 \ ft=119.4 \ ft\]
Determine elevation at BM:

\[BM=HI_1-BS_1\]
\[BM=119.4 \ ft-4.6 \ ft\]
\[BM=114.8 \ ft\]
 

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