Nikon DTM-502 Series Instruction Manual page 124

Menu
2:Dist
As the surface of the earth is curved, the vertical difference (VD and
Z) at the measurement point, as referenced to the horizontal plane,
will inevitably include some error. This error is called curvature
error. Likewise, as the density of the air surrounding the earth
decreases with altitude, light is refracted when it passes through the
air. The subsequent error caused by this refraction is called
refraction error.
Curvature error (A A')
Item
Scale Factor
Numerical input between
0.999600 and 1.000400.
Temp&Press Correction
ON/OFF
Sea Level Adjustment
ON/OFF
C&R Correction
OFF: C&R OFF
0.132: C&R ON (coef. 0.132)
0.200: C&R ON (coef. 0.200)
Refraction error (AI AI')
P A'
Horizontal
direction
A
O
Conditions
AI'
AI
A'
P
3-98
3