Surveying - Carpenter's and Builder's Math, Plans, and Specifications - page 208

Ta ble 6-1 Field Notes (Corresponding to the Operations
Illustrated in Figure 6-6)
Height of
Station Distance Backsight Instrument Foresight Elevation Remarks
A0 4.2 104.2 ..... 100.0 Bench mark,

top of hyd-
rant.Turning
point

B 100 ..... ..... 10.1 94.1

C60 ..... ..... 7.3 96.9

D 0 ..... ..... 5.8 98.4

T ..... 4.1 99.1 9.2 95.1

E70 6.8 ..... ..... 92.3

F 110 ..... ..... 9.5 89.6

G 0 ..... ..... 11.5 87.6

1. Assume a datum or reference line below the elevation of the
lowest station, and refer all elevations to this line. Start at some
permanently fixed point (such as a mark on a building or the
top of a hydrant). This is called a benchmark .
2. Let A in Figure 6-6 be the benchmark, and assume a datum
line 100 feet below the level of A .
3. Start with the instrument between A and B , and take a back-
sight on A . The distance Aa is found to be 4.2 feet, which,
when added to 100 feet, gives the height of the instrument.
4. Next, take foresights on B ,

C , and D , and record these read-
ings in the proper column. Readings Bb, Cc , and so on, sub-
tracted from the height of the instrument, will give the ele-
vations at B C , and so on. This is done, and the results are

recorded in the proper column of field notes.
5. The ground falls away so rapidly beyond D that it is necessary
to set up the level farther along and, therefore, establish a
new height of instrument. This is done by holding the rod
at some convenient point (such as at T ) called the turning
point , and taking a foresight, which measures the distance Tt
(9.2 feet).
6. The level is then set up in its second position between E and
F , and a backsight is taken on the rod in the same position,
which gives the distance Tt (4.1 feet).
7. The distance t t then equals 9.2

,

5.1 feet, and this is
subtracted from the previous height of instrument, thus giving
the new HI , that is 104.2

− 4.1 =

− 5.1 = 99.1 feet.