System Accuracy
Several factors can influence the system's accuracy for determining the location of a prism:
• Internal ATR/ATRplus accuracy
• Angular accuracy of the instrument
• Type and centring accuracy of the prism
• Selected EDM measuring program
• External measuring conditions
Therefore, the overall pointing accuracy of the determined point location can be lower than the given angular accuracy and the ATR/ATRplus accuracy. The following paragraphs provide a short overview of these influencing factors and their possible intensities.
Angular accuracy
The accuracy of angular measurements depends on the instrument type. The angular accuracy for total stations is typically in the range from 0.5² to 5². The resulting error depends on the measurement distance.
➜ Refer to the data sheet of the respective instrument model for information about the angular accuracy.
EDM accuracy
The distance measurement accuracy consists of two parts: a fixed value and a distance-dependent value (ppm-value).
Example: "Single measurements: 1 mm + 1.5 ppm"
The EDM accuracies for prism and reflectorless measurements can differ. Additionally, the accuracies can differ depending on the used technologies.
➜ Refer to the appropriate data sheet for information about the EDM accuracy.
ATR/ATRplus accuracy
Automatic target aiming accuracies, like those of the ATR/ATRplus, are in general the same as the stated angular accuracy. Therefore these accuracies are also distance-dependent parameters.
External impacts, like heat shimmer, rain (prism surface covered by rain drops), fog, dust, strong background lights, dirty targets, alignment of the targets etc. can have a significant influence on the automated target. In addition the selected EDM mode affects the ATR/ATRplus performance. Under good environmental conditions and with a clean, properly aligned target the accuracy of the automated target aiming is equivalent to the manual target aiming (presumed valid calibration values).
Type and centring accuracy of the prism
The prism centring accuracy depends mainly on the used prism type, for example:
➜ Refer to the white paper "Leica Surveying Reflectors" for information about the different centring accuracies.
Additional influencing factors
When determining absolute coordinates, the following parameters can also affect the resulting accuracy:
• Environmental conditions: temperature, air pressure and humidity
• Typical instrument errors, such as horizontal collimation error or index error.
• Proper functioning of laser plummet or optical plummet
• Correct horizontal levelling
• Setup of the target
• Quality of additional equipment, such as tribrach or tripod.
Telescope
Compensator
Level
Four button keyboard unit 
Instrument ports 
Pin Assignments of the 5 Pin LEMO-0 Port
Instrument dimensions
With CCD18
Weight:
Instrument (including battery): 5.0 kg
Tribrach: 0.8 kg
Laser plummet 
Drives
Motorisation
Power
Internal battery 
External battery 
Environmental specifications
Reflectors
There are no special prisms required for ATR/ATRplus or for SpeedSearch /PowerSearch.
Electronic Guide Light (EGL)
Working range: 5 m to 150 m (15 ft to 500 ft)
Position accuracy: 5 cm at 100 m (1.97" at 330 ft)
Automatic corrections: The following automatic corrections are made:
• Atmospheric correction.
• Reduction to mean sea level.
• Projection distortion.
Atmospheric correction DD1: The slope distance displayed is correct if the scale correction in ppm, mm/km, which has been entered corresponds to the atmospheric conditions prevailing at the time of the measurement.
The atmospheric correction includes:
• Adjustments for air pressure
• Air temperature
• Relative humidity
For highest precision distance measurements, the atmospheric correction should be determined with an accuracy of 1 ppm. The following parameters must be redetermined:
• Air temperature to 1 °C
• Air pressure to 3 mbar
• Relative humidity to 20%
Air humidity: The air humidity influences the distance measurement if the climate is extremely hot and damp.
For high precision measurements, the relative humidity must be measured and entered along with the air pressure and the temperature.
Air humidity correction 
Index n 
The index n is calculated from the formula of the IAG Resolutions (1999), and is valid for:
Air pressure p: 1013.25 mbar
Air temperature t: 12 °C
Relative air humidity h: 60%
Formulas
Formula for visible red laser
· 10x 4.126 · 10-4 · h - 0.29535 · p ΔD1= 286.338 -
002419_002
DD1 Atmospheric correction [ppm]
p Air pressure [mbar]
t Air temperature [°C]
h Relative humidity [%]
a
1
273.15
x (7.5 * t/(237.3 + t)) + 0.7857
If the basic value of 60 % relative humidity as used by the EDM is retained,
the maximum possible error in the calculated atmospheric correction is 2 ppm,
2 mm/km.
Reduction to mean sea level DD2
The values for DD2 are always negative and are derived from the following
In countries where the scale factor is not unity, this formula cannot be directly applied.
Atmospheric corrections °C
Atmospheric corrections in ppm with temperature [°C], air pressure [mb] andheight [m] at 60% relative humidity.
Atmospheric corrections °F
Atmospheric corrections in ppm with temperature [°F], air pressure [inch Hg] and height [ft] at 60% relative humidity.
