Zoom20/30/35 Pro | 96Technical Data
Atmospheric correction
°F
Atmospheric corrections in ppm with temperature [°F], air pressure [inch Hg] and height [ft] at 60 % rela-
tive humidity.
15.8 Reduction Formulas
Formulas
The instrument calculates the slope distance, horizontal distance, and height difference in accordance with
the following formulas. Earth curvature (1/R) and mean refraction coefficient (k = 0.13) are automatically
taken into account when calculating the horizontal distance and height difference. The calculated hori-
zontal distance relates to the station height and not to the reflector height.
Slope distance
Horizontal distance
Height difference
130°F
120°F
110°F
100°F
90°F
80°F
70°F
60°F
50°F
40°F
30°F
20°F
10°F
0°F
-10°F
-20°F
130°F
120°F
110°F
100°F
90°F
80°F
70°F
60°F
50°F
40°F
30°F
20°F
10°F
0°F
-10°F
-20°F
16
[ ft ]
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 inch Hg
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 inch Hg
16000
15000
14000
13000
12000
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
o ft
-15
-20
-25
-30
-35
-40
-45
-50
-55
-10
-5
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
aMean Sea Level
b Instrument
cReflector
SD Slope distance
HD Horizontal distance
VD Height difference
SD Displayed slope distance [m]
D0 Uncorrected distance [m]
ppm Atmospheric scale correction [mm/km]
mm prism constant [mm]
HD Horizontal distance [m]
YSD * sinζ
XSD * cosζ
ζ = Vertical circle reading
A (1 - k/2)/R = 1.47 * 10
-7
[m
-1
]
k = 0.13 (mean refraction coefficient)
R = 6.378 * 10
6
m (radius of the earth)
VD Height difference [m]
YSD * sinζ
XSD * cosζ
ζ = Vertical circle reading
B (1 - k)/2R = 6.83 * 10
-8
[m
-1
]
k = 0.13 (mean refraction coefficient)
R = 6.378 * 10
6
m (radius of the earth)
c
a
b
SD
VD
HD
SD
= D
0
· ( 1 + ppm · 10
-6
) + mm
HD
= Y - A · X · Y
VD
= X
+ B · Y
2
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