Total station surveying principles and equipment setting up.

1. TOTAL STATION

2. CONTENTS
• ELECTRONIC DISTANCE MEASUREMENT
• PARTS OF A TOTAL STATION
• ACCESSORIES
• ADVANTAGES AND APPLICATIONS
• INTRODUCTION TO ASTRONOMICAL TERMS
• FIELD PROCEDURE FOR TOTAL STATION SURVEY

3. ELECTRONIC DISTANCE
MEASUREMENT
• Method of measuring distance between points electronically by using
electro magnetic waves (Infra red, Micro waves etc…)
• Microwave requires transmitters/receivers at both ends
• Infra red use a transmitter at one end and a reflecting prism at the other
end (Most commonly used)
• EDM devices are typically mounted on top of a theodolite, but can
directly mounted on to a tribrach
For Eg. Total Station is a combination of theodolite with built in EDM
and Microprocessor

4. • WORKING PRINCIPLE
• EDM is very useful in measuring distances that are difficult to access
and are long distances.
• It measures the time required by a wave to be sent to a target and
reflect back

5. Measurement of distance
• Two Methods
1. Pulsed laser system
2. Phase shift Method (Most commonly used)
• Pulsed Laser System
• Make uses pulses derived from an infra red/ visible laser diode
• Distance is obtained by measuring transit time and velocity of pulsed electro
magnetic signal in travelling between TS & target and back
• Velocity V of pulses gets determined
• Transit time t is measured using electronic signal processing technique
• Distance, D = 0.5 * V * t
• Large no. of pulses gets analyzed during measurements

6. • PHASE SHIFT METHOD
• Uses continuous EM waves
• Measures length by indirectly determining the number of full and partial
cycles of transmitted E M between the two ends of a line
• EDMI (Electronic Distance Measuring Instrument) consisting of an electro
wave generator, an oscillator , a modulator, a transmitter, and a receiver etc..
• Modulated EM Wave is transmitted to the target , Placed at the other end of
the line. The target, acting as a reflector, reflects the light beam back to the
receiver , where the incoming light is converted to an electrical signal. A
phase comparison is made between the projected and reflected signals. Then
the amount by which the transmitted and received signals are out of phase
gets measured electronically and get registered in a meter by getting
converted to an equivalent distance.

7. PHASE SHIFT METHOD
• If the received signal is out of phase by a measure of Dq , Then the
equivalent distance, d is
• d = Dq * l/360
l : Wavelength of the E M wave
• The distance is calculated as
D =
1
2
*[ nl + (
Dq
360
) l]
n : integral no . of wave length, l in the double path ( see next figure)

9. TOTAL STATION

10. TOTAL STATION
• An electronic / Optical Instrument
• An electronic theodolite having optical telescope integrated with
EDM (Electronic Distance Meter) and Microprocessor with
memory unit and other accessories
• Accessories consists of Keyboard , Display , Power Supply ,
data collectors, field computers, memory card etc…
• Provides (By measuring or estimating)all parameters
(Distances&Angles) & derived values (corrections & cordinates)
of surveying simultaneously
• Values of parameters can get displayed in viewing panel
• Precision may vary from 0.1” to 20”

11. TOTAL STATION TYPES
• Based on minimum circle reading accuracy :
0.1” to 20” (For eg: 1” total station, 2” total station, 5”, 15” , 20”
etc..)
• Based on Control
• Manual
• Robotic : (Operator controls from distance via remote)

12. PARTS OF A TOTAL STATION

14. SCREEN AND KEYS

15. WORKING OF SALIENT PARTS
• Handle : To carry the Instrument physically
• Bluetooth antenna : To communicate via Bluetooth wireless
technology
• External interface hatch : To connect to external devices
• Instrument height mark : To measure height of Instrument
• Luminance sensor : Adjusts the brightness of screen automatically
• Guide light : To carry out setting out measurement effectively
• Objective lens :
• Laser pointer function : To sight a target in dark location
• Vertical clamp screw :
• Vertical fine motion screw

16. • Trigger key: To carry out operation indicated by the soft key in bold
type on the screen
• Horizontal clamp screw:
• Horizontal fine motion screw:
• Tribrach clamp: clamp the upper part of the instrument with lower part
• Telescope eyepiece screw:
• Telescope focusing ring:
• Sighting collimator : To aim in the direction of measurement point
• Instrument centre mark

17. • A Total Station primarily consist of an electronic theodolite, an EDM,
Microprocessor and many other accessories
• Body of a theodolite is divided into two broad parts, upper part -The
Alidade & lower part – The Tribrach
• Alidade includes standards, telescope,EDM, Circles (horizontal &
vertical) and other elements for measuring angles and distance
• Tribrach contains foot screws, circular level, clamping devise and
treads

18. • TELESCOPE
• Objective lens : focus on the object to form image at the plane of reticle
• Eyepiece lens : focus on the plane of reticle
• Axis or line of sight : Line joining the objective lens and the eyepiece
lens
• Parallax : If there is relative motion between Image formed & reticle,
parallax is present which should be avoided
• Lock & tangent screws for revolutions & rotations
• AUTOFOCUS
• It makes the telescope focus automatically to target. After aiming the
telescope to the target, autofocus button gets pressed

19. • ANGLE MEASUREMENT SYSTEM
• For horizontal angle measurement, two glass circles within the
alidade are mounted parallel one on the top of other , with a slight
spacing between them. In a levelled TS (Total Station) horizontal
angle circles should be in horizontal plane
• For vertical angle measurement, two more glass circles are
mounted in parallel with slight spacing between them but aligned in
a vertical plane automatically in a levelled TS

20. • MICROPROCESSOR
• Controls , measures , computes , Reduces observations/ data by
providing commands through keyboard.
• Some salient functions
• To make circles zeroed instantaneously
• To observe angles by method of reiteration in either direction
• To observe angles by method of repetition
• Averaging multiple distances and angle observations
• Reducing slope distances into horizontal & vertical distances
• Computation of elevation from vertical distance components
• Computation of coordinates from horizontal angle and
horizontal distance components

21. • AUTOMATIC COMPENSATOR
• To get TS precisely indexed with the direction of gravity
• Automatically align vertical circles having zero degree oriented
precisely upward towards the zenith.
• PLUMMET
• Build into either alidade or tribrach
• Provides a line of sight that is directed downwards , collinear with
the vertical axis after leveling
• For accurate centering
• Laser variety provides a beam of collimated light

22. • OPTICAL GUIDANCE SYSTEM
• One or two above or below the telescope tube at the end of the objective
lens. These are light emitting diodes and emit a visible light pattern which
enables a detail pole to be set directly on the line of sight and at the correct
distance without the need for hand signals from the total stations
• In some instruments , OGS is represented as Guide Light . It is composed of
lights that is divided into Green and Red sections. A poleman can ascertain
the present position by checking the Guide light color as follows
LIGHT STATUS MEANING
Increased flashing speed Move towards TS
Decreased flashing speed Move away from TS
Fast Flashing Target at the correct distance
Red Move target left
Green Move target right
Red & Green Target at correct horizontal position

23. ACCESSORIES
• INTRODUCTION
Apart from salient components, some accessories are required for working
with TS. Some of the Accessories are present as integral part of the TS –
Control Panel , Data Collector , Memory Etc…
Some others totally independent – Reflectors
These are the Major accessories
• CONTROL PANEL
• DATA COLLECTORS
• MEMORIES
• REFLECTORS
• SOFTWARE

24. ACCESSORIES - CONTROL PANEL
• Control panel of a total station consist of a keyboard & multiple line
LCD ( liquid Crystal Display)
• The keyboard enables the user to select & implement different
measurement modes, enable instrument parameters to be changed and
allow special software functions to be accessed. Multifunction keys in
the keyboard carry out specific tasks and some other keys activate&
display menu systems which enable the TS to be used as computer
• Keyboard is also used to code data generated by the instrument for
mapping. If a code is entered from the keyboard to define the feature
being observed, the data can be processed much more rapidly when it
is downloaded into and processed by an offline based computer
plotter.

25. • The keyboard and display can be detached from the instrument and
interchanged with other total stations and with GPS receiver. This
enables data to be shared between different instruments and systems
using single interface
• Thus combination of keyboard and display unit not only controls the
operations of total station but also stores measurements and data

26. • KEYBOARD
• Keyboard contains different types of keys to provide different commands to
its micro processor which subsequently gets works carried out by its
different parts. It contains different alpha numeric keys , option selection
keys, switching keys, Power key , lighting keys etc..
• Salient Keys
• Power Key : To switch between ON & OFF
• Illuminator Key : For lighting the reticle/keys and to select screen backlight
brightness . To turn laser- pointer/guide light ON /OFF
• Star Key : To jump from each mode screen to the screen of
checking/changing the various settings directly
• ESC Key : To cancel the input data/to return to previous screen
• TAB Key : To shift to next item

27. • B.S Key : Delete a character on the left
• S.P Key : Input a blank space
• FUNC Key : To toggle between observation mode screen pages
• ENT Key : Select/Accept input word/Value
• Numeric – Alpha Keys : To input numerals and alphabetic characters
• α key : Input Mode Key (To switch between numeric and alphabetic
characters)
• SHIFT Key : To switch between lower case and uppercase characters
• Target Keys : To switch between target types (Reflector & Non Reflector)
• PRG Key : To switch between program mode and basic mode
• Luminance sensor/ Microphone key

28. ACCESSORIES - DATA COLLECTOR
• Automatically receives and stores field notes in computer
compatible files
• Control of the measurement and storage operations is
maintained through data collector’s keyboard
• Point identifiers and other descriptive information with
measurements may be recorded
• Preliminary information required to be entered manually before
the collection of measurements
• For a given type of survey, data collector is programmed to
follow specific steps
• Stores information in either binary or ASCII format

29. • Data storage and entry are carried out through a series of step
by step instructions displayed by the data collector
• Enable operator to scroll through stored data, display for review
and editing in real time
• Data collectors are developed instrument specific, however
there are some which are flexible
• Data collectors are of two types , External and Internal

30. • EXTERNAL DATA COLLECTOR
• Can be interfaced with various instruments
• Has Windows CE OS , thus can run variety of windows software
programs
• Can do variety of calculations directly in the field
• Has Bluetooth technology to communicate with other instruments and
WiFi capabilities for connecting to internet

31. • INTERNAL DATA COLLECTOR
• Data collection system as internal components directly into the
equipment
• Incorporates all features of external data collectors
• Use Windows CE OS
• Pen & Pad arrangement /Key board is used to point on menus and
options to run software

32. ACCESSORIES –DATA COLLECTOR…
• ADVANTAGES
• Mistakes in reading and manually recording observations are precluded
• Time to process , display and archive the field notes in office reduced
significantly
• Execute program in field and in real time
• Most useful when large quantities of information is involved
• DISADVANTAGES
• Field data may be erased due to carelessness or malfunction of instruments
• All information can not be entered/stored in digital form
• Varied data structures from different manufacturers
• Need to be compatible to the computer/software in which data need to be
considered further.

33. ACCESSORIES - MEMORIES
• Total station makes use of internal memories or memory cards for
processing and storing information
• Internal memory on board storage capacity of about 5000 to 10000
coded survey points
• Data can also be stored on memory cards which are plugged into Total
Station
• All memory cards should satisfy PCMCIA standards
• Data may get exchanged to/from PC from/to through card reader

34. ACCESSORIES - REFLECTORS
• TS Use return or reflected signals for measurements. This is obtained
by using a specific reflector
• TS reflectors consist of special reflecting prism constructed from glass
cubes or blocks
• Return waves or pulses along a path exactly parallel to the incident
path but within a range of angles of incidence of about 20 degree
• A wide range of reflecting prisms are available to suit short as well as
long range measurements
• Single & Triple prism sets for fixing on tripod stand ,mini-prism for
pole mounting or 360 degree prism for robotic TS are being used
• Reflecting prisms are associated with a prism constant (distance
between effective centre of the prism and its plumbing point) of the
order of -30 to -40 mm

35. ACCESSORIES - SOFTWARE
• Operating System generally used is Windows CE
• Field Software or the measurement software . Field softwares are
manufacturer dependent
• Processing softwares : These are which is made use to arrive at the
final product of the data collected.
Eg : Carlson , AUTOCAD, etc…

36. ADVANTAGES OF TOTAL STATION
• Quick setting of the instrument on the tripod using laser plummet
• On-board area computation program to compute the area of the filed
• Local language support
• Full GIS creation
• Automation of old maps
• Greater accuracy in area computation
• Graphical view of plots and land for quick visualization
• Integration of data base
• The area computation at any user required scale

37. • Once the field jobs are finished , the map of the area with
dimensions is ready instantly after data transfer
• It reduces the time taken for the survey considerably and it also
able to measure up to 3 to 5 km distances.
• Comparatively easy to work with
• High precision

38. APPLICATIONS OF TOTAL STATION
• To measure horizontal and vertical angles
• To obtain the horizontal distance, inclined distance and vertical
distance between points.
• To get the three-dimensional co-ordinates i.e.[x,y,z] of a point in
space.
• To find the length of a missing the line
• To find the elevation of the remote object.
• To find the distance to a remote object
• To locate the points at a predetermined distance along gridlines.
• Calculation of Area of a closed figure.

39. • Total station is extensively used in Mine Survey, Cadastral
Survey, Engineering Survey, Large scale Survey, Road / rail/
canal Survey
• Some total stations also have a GNSS (Global Navigation
satellite System) interface which combines the advantages of
these two technologies (GNSS – line of sight not required
between measured points; Total Station – high precision
measurement especially in the vertical axis compared with
GNSS) and reduce the consequences of each technology’s
disadvantages (GNSS – poor accuracy in the vertical axis and
lower accuracy without long occupation periods; Total Station –
requires line of sight observations and must be set up over a
known point or with line of sight to 2 or more points with known
location).

40. DISADVANTAGES OF TOTAL STATION
• It may be difficult for the surveyor to look over and check the
work while surveying.
• The instrument is costly. And for conducting surveys using Total
station, Skilled personnel are required.
• For an over all check of the survey, It will be necessary to return
to the office and prepare the drawings using appropriate
software
• The instrument contains sensitive electronic assemblies which
have to be well protected against dust and moisture

41. PRECAUTION TO BE TAKEN WHILE
USING A TOTAL STATION
• Use both hands to hold the total station handle
• Set up the tripod as stable as possible
• Do not move or carry a tripod with the Total Station fixed on it ,
except for centering
• Store the battery pack with the battery discharged
• Do not over tighten any of the clamp screws
• Take maximum care when the tribrach is removed from the
Total Station

42. FIELD PROCEDURE FOR TOTAL
STATION SURVEY
• Leveling the Total Station
• Leveling the Total Station must be accomplished to sufficient accuracy
otherwise the instrument will not report results
• Leveling the instrument takes 30 to 45 minutes – make sure you can
see all targets from the instrument station before going through the
process

43. • STEP 1 : TRIPOD SETUP
• Tripod legs should be equally
spaced
• Tripod head should be
approximately level
• Head should be directly over
survey point

44. STEP 2: MOUNT INSTRUMENT ON TRIPOD
• Place Instrument on Tripod
• Secure with centering screw
while bracing the instrument
with the other hand
• Insert battery in instrument
before leveling

45. STEP 3: FOCUS ON SURVEY POINT
• Focus the optical plummet
on the survey point

46. STEP 4: LEVELING THE INSTRUMENT
• Adjust the leveling foot screws
to center the survey point in the
optical plummet reticle
• Center the bubble in the circular
level by adjusting the tripod legs

47. STEP 4: LEVELING...
• Loosen the horizontal clamp and turn instrument until plate level is
parallel to 2 of the leveling foot screws
• Center the bubble using the leveling screws- the bubble moves toward
the screw that is turned clockwise
• Rotate the instrument 90 degrees and level using the 3rd leveling screw

48. STEP 4: LEVELING…
• Observe the survey point in the optical plummet and center the
point by loosening the centering screw and sliding the entire
instrument
• After re-tightening the centering screw check to make sure the
plate level bubble is level in several directions

49. STEP 5 : ELECTRONICALLY VERIFY
LEVELING
• Turn on the instrument by pressing and holding the “on” button (you
should hear an audible beep)
• The opening screen will be the “MEAS” screen. Select the [Tilt]
function
• Adjust the foot level screws to exactly
center the electronic “bubble”
• Rotate the instrument 90 degrees and
repeat

50. STEP 6: ADJUST IMAGE & RETICLE FOCUS
Release the horizontal & vertical clamps and point telescope to a
featureless light background
• Adjust the reticle (i.e. cross-hair) focus adjustment until reticle image is
sharply focused
• Point telescope to target and adjust the focus ring
Until target is focused
• Move your head from side-to-side to test for image
shift (i.e. parallax). Repeat the reticle focus step if
parallax is significant
• NOTE: When the instrument operator changes the
reticle focus may need to be adjusted

51. MEASURING THE HEIGHT OF AN OBJECT
• Level the instrument at a site where the target can be viewed through the
telescope and the mirror target can be setup directly below the target
• After powering on the instrument select “REM” from “MEAS” > “Menu”
• Ht = h1 + h2
• h2 = S (sin θz1) (cot θz2 ) – S (cos θz1)
• NOTE: Instrument height does not affect this calculation

52. MEASUREMENT OF TARGET HEIGHT
• Set the Target Height from “MEAS” > “Menu” > “Coordinate” > “Station Orientation” >
“Station Coordinate”
• Set the target height to the measured height of the mirror target. Make sure you use
the metric side of the tape measure if working with metric units. You do not have to fill
out the other fields for a REM measurement, however, it is good practice to measure
and enter the instrument height. After entering the TH and IH make sure you press
“OK” (F4) to accept new values.
• Press “ESC” to return to the “MEAS” menu
• Select the “MEAS” > “Menu” > “REM”, sight the mirror target,
press [OBS] to measure “S”, then [STOP]
• Sight the object above the target for height measurement
• Select [REM] after sighting the top of the height target,
and then [STOP] to stop the calculations

53. REM SCREEN RESULTS
• To re-shoot the mirror target use the [OBS]
on the REM screen.
• Note that after selecting REM the instrument
continues to make calculations in case you
need to adjust the vertical angle on the height
target.
• Select “STOP” to terminate calculations on the
REM command.

54. Trouble-Shooting the REM Measurement
• The only numerical input is the target height so make sure that is entered
correctly. When TH is changed make sure you hit the “OK” function key.
• If the instrument is reset (zeroed) TH will be 0.0 so if you make a REM
measurement with TH=0 the answer will be underestimated by the actual
TH.
• A quick check can be made by using REM on the mirror target – the
answer should be the TH.

55. CALIBRATING THE INSTRUMENT
• Calibration must be completed before coordinates can be obtained
• 3 possible calibrations:
• Backsight by angle: must know instrument coordinates and have
a landmark/target at a known azimuth
• Backsight by coordinate: must know instrument coordinates and
have mirror target set on a position of known coordinates
• Resection (triangulation): must have 3 or more mirror targets
established at known 3D coordinates

56. 3D COORDINATES
• Coordinates may be absolute or relative depending on survey
requirements
• Surveying the area of a mining site would require relative coordinates,
therefore, the initial instrument X,Y,Z coordinates may be 5000, 5000, 100
• Surveys that have to match a downloaded aerial photo from the USGS
would have to match UTM NAD83 coordinates so the starting point would
have to be determined by an accurate GPS receiver

57. Calibrate by Backsight by Angle
• Remember that when the instrument is powered on it has a random
X,Y coordinate system: you must align the instrument with your working
coordinate system.
• Level the instrument on the desired starting survey marker. Make sure
that on the last leveling step the optical plummet is centered on the
survey point
• Measure the target height and instrument height
• Select [COORD] from the MEAS menu
• Select “Stn. Orientation” and then “Stn. Coordinate”
• Edit the “N0”, “E0”, and “Z0” fields to appropriate values (i.e. northing,
easting, elevation of instrument)

58. Backsight by Angle continued..
• Enter the instrument and target height if necessary
• Select [OK] when done

59. Backsight by Angle continued…
• Select “Backsight” and then “Angle”
from the menu
• Sight the landmark/target of known azimuth
relative to instrument with telescope
• Select “Angle” from menu. Note that the menu
displays the zenith angle (ZA) and current horizontal
angle (HAR) and is waiting for you to enter the known
angle with [EDIT]
• Note: if you enter an azimuth angle as “85.4514” this
will be interpreted as 85 degrees, 45 minutes, 14 seconds
• IMPORTANT! You must select [OK] to accept the angle.
• Never use <Esc> to leave this screen

60. Backsight by Angle Continued…
• NOTE: because the backsight by angle simply sets the instrument
horizontal angle encoder to match your desired coordinate system the
mirror target is never “shot” by the beam. If you can accurately sight on an
object or landmark such as a building corner the mirror target is not
needed. Make sure the instrument is “locked” and accurately sighted with
telescope before entering the backsight angle.
• Because there is no internal statistical measure of how well the backsight
angle has been set it is imperative to check the backsight independently:
• Known point: shoot the target at a position of known X,Y,Z such as a
GPS point. The result should be within the resolution of the GPS.
• Known angle: shoot to a landmark at a known azimuth from the
instrument location- the angle should be within the resolution of the
instrument

61. Backsight by Coordinate
Use this method when you have 2 known survey points with the instrument established
on one and the mirror target on the other survey point
• From the “MEAS” menu select [COORD] and then “Stn. Orientation”. Set the
instrument coordinates with “Stn. Coordinate” and then select [OK] and return to
“Backsight”
• Select “Coord” and then enter the backsight target
coordinates (NBS, EBS, ZBS) and select [OK]
• Sight in the target and inspect the “Azmth” (it should
be reasonable for your coordinate system).
• Select [YES] to calibrate. If you don’t select [YES] the
coordinate system is still random

62. Backsight by coordinate …
• Always check the calibration of the instrument by shooting the target
used for the back sight.
• The resulting X,Y,Z should be within the several cm resolution typical for
a TS instrument.
• It is a very good idea to shoot other benchmarks within range to make
sure accuracy is within acceptable limits

63. RESECTION
• Resection uses 3 or more known target survey points to automatically
determine the X,Y,Z coordinates of the instrument
• This has the significant advantage of not requiring the instrument to be
leveled exactly on a survey point- any convenient location where you can
sight the targets is OK
• The ideal geometry is displayed
to the right

64. Resection continued…
Prior to resection enter survey markers as known points through the “MEM” menu
• From the “MEAS” menu select “[MENU]” > [RESEC]
• The resection procedure requires that the known
coordinates be defined first, and in the order that
they will be shot
• In the top right screen the 1st point has been defined
and the 2nd point is being entered. You can use
[READ] to read in previously entered or measured points
• Press the “>” or “<“ arrow to move to next or previous
point
• When all points are entered select [MEAS]

65. Resection continued…
• The [MEAS] screen (right) displays the
point being shot – in this example the
1st point
• Choose [DIST] if you are shooting to a
mirror target, [ANGLE] if not
• Select [YES] to accept measurement,
[NO] to re-shoot, [EDIT] to change target
height
• The [CALC] option will be displayed when
the standard deviation of northing and easting
can be displayed

66. Resection continued…
• Press [CALC] or [YES] on last point to display the calculated instrument
coordinates and the standard deviation of easting (σE) and northing (σN). Press
[OK] to finish Resection, and then [YES] to set the backsight azimuth to the
1st shot point
• Press [RESULT] to display the residuals of each shot
point- large deviations identify “bad” points
• If there are no problems press {Esc} to return to main
resection screen
• The standard deviations are a measure of the accuracy.
They should be in the range of several cm’s for most
surveys

67. Resection Notes
• Resection initializes the X,Y,Z coordinates of the instrument. Save this
as a point (ex. G1S02 for group 2, instrument station #2) since it
represents a surveyed coordinate
• Once the instrument is calibrated the mirror targets can be taken down
and used elsewhere
• The instrument height should be entered before resection is calculated
• You can only begin shooting resection point 1 from the resection point
#3 or higher coordinate entry screen

68. Resection Notes
• Certain Geometries
should be
avoided: Targets
and Instrument
should not be
arranged
on a circle

69. Coordinate Measurement
• Used to determine XYZ coordinates of
target point.
• Make sure the instrument height and
target height are already set.
• Make sure backsight/resection have
already “locked” the instrument into a
mapping coordinate system
• From MEAS select
Menu > Coord > Observation

70. Offset: Single Distance
• Single distance offset – used to measure points that cannot be
“occupied” by the target.
• Examples:
• center of a large tree,
• center of a fountain
• center of a building

71. Offset: Single Distance
• Offset point can be right or left of the target, but must be the same
distance from the instrument.
• Offset point can be in front or behind target, but must be on the
same azimuth line.
• In any case the person/team holding the target must have a tape to
measure the exact distance (to cm accuracy at least) of the offset.
• The instrument will request an observation to the target first, and
then request the offset distance and where the target point is relative
to the point of interest (left, right, front, back).

72. Offset: Single Distance
• Note the arrow that indicates that
the target is to the left of the survey
point by 2 meters.