Sokkia 30R Series Operator's Manual page 122

24. CHANGING THE SETTINGS
Temp. (Temperature): -30 to 60°C (15*)
Air pressure: 500 to 1400hPa (1013*), 375 to 1050mmHg (760*)
ppm (Atmospheric correction factor): -499 to 499 (0*)
Illum. hold: Laser (laser sight)* / Guide (Guide light)
• The screen will be displayed only when "Illum. hold " is set to "Guide" and the
cursor is on "Guide".
Item set and option (*: Factory setting)
The Guide light (Brightness level of the guide light): 1 to 3 (3*)
Atmospheric correction factor
The SET measures the distance with a beam of light, but the velocity of this
light varies according to the index of refraction of light in the atmosphere.
This index of refraction varies according to the temperature and air
pressure.
• To precisely determine the atmospheric correction factor, the average
temperature and air pressure along the measurement beam route must be
taken. Take care when calculating the correction factor in mountainous
terrain as the difference in height will result in differences in atmospheric
conditions between two points.
• The SET is designed so that the correction factor is 0 ppm at an air pressure
of 1013 hPa and a temperature of 15°C.
• By inputting the temperature and air pressure values, the atmospheric
correction value is calculated and set into the memory. Calculate the
atmospheric correction factor as shown in the following formula.
ppm = 282.59 -
"30.2 Atomospheric Correction for High Precision Distance
Measurement"
• If the weather correction is not required, set the ppm value to 0.
114
Illum.hold: Guide
Guide light: 3
0.2942 x air pressure (hPa)
1 + 0.003661 x air temperature (°C)