Topcon AT-G4 - Measuring a Horizontal Angle; Stadia Surveying

also the difference in elevation or height (h}, or
h = bA- fB.
The height from . the base surface or level, in th is case,
can be obtained from the formula -
Hs = HA + h
2. Measuring a Horizontal Angle
The AT- G series has a horizonta l circle .whi ch can be used
for measuring an angle.
The horizontal circle is graduated in one degree ( 1 g)
divisions but numbered every 10 degrees (1 og}, with the
scale calibrated from 0 to 350° (0 to 390g}, with the
value increasing as the i nstrument is revolved clockwise.
1} First, set up and proper ly level the instrument at the
starting point, say, Point C.
Then, sight through t he telescope on the base target,
say, Point A. Align the rod set up on top of Point A
precise ly to the ver tical cross-hair line of the te le-
scope reticule with the fine horizontal knob.
Then, rotate the horizontal c i rcle ring to make zero
setting of the scale.
2} Next, si ght through the telescope on a rod held on
top of Po i nt 8 and precise ly al ign with the fine hori-
z ontal knob. The reading at this t i me will, of course,
be the horizontal angle between Points A and B, from
Point C, or the ang le ACB.
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P oint A Point B
Po int(A} D T Point(B )
egree ype
10 0 390
• •••••
• ••
Point(A} G d T Point(B }
ra e ype
3. Stadia Surveying
The AT - G Series Auto-Levels can be used for stadia sur-
veying, which is simply a convenient method for measur -
ing distances with t he stadia hairs of the instrumen t, in
combination with a graduated rod, such as leveling rod or
stadia rod (which is preferable for l ong distances}.
The distance from the center of the instrument to the rod
is found by sighting through the i nstrument on to the rod
and multiplying the stadia interval or reading (i. e., the
interva l between the apparent locations of the bottom and
top stadia hairs on the rod} by 100.
1«- --L = I 00 2 -- ~
1) Fir st , set up the rod on the point .
2)
Then, sight through the tele s cope of the properly
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