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Which of the following tacheometer constant ?
Additive
Multiplying
Both A and B
None of these
Both A and B
In tacheometric surveying, a tacheometer is fitted with an anallatic lens to measure distances optically without using a measuring tape. The instrument uses two constants: the multiplying constant (K) and the additive constant (C). Therefore, both multiplying and additive constants are tacheometer constants, making Option C correct.
In tacheometric surveying, a tacheometer is fitted with an anallatic lens to measure distances optically without using a measuring tape. The instrument uses two constants: the multiplying constant (K) and the additive constant (C). Therefore, both multiplying and additive constants are tacheometer constants, making Option C correct.
D=K⋅s+C — General tacheometric distance equation
K=if — Multiplying constant
C=f+d — Additive constant
The distance measurement in tacheometry relies on the principle of isosceles triangles. The distance equation is given by D=K⋅s+C, where K is the multiplying constant (K=if) and C is the additive constant (C=f+d). Here, f is the focal length of the objective lens, i is the stadia hair interval, and d is the distance from the vertical axis of the instrument to the objective lens.
For an ordinary tacheometer, the typical value of the multiplying constant K is 100.
For an ordinary tacheometer, the additive constant C usually ranges between 30 cm and 45 cm (0.3 m to 0.45 m).
When an anallatic (or anallactic) lens is fitted, the additive constant C is reduced to zero (C=0).
Allows rapid distance and elevation measurements without direct taping.
Ideal for steep, rough, or inaccessible terrains where chaining is difficult.
Lower precision compared to direct precise chaining or EDM devices.
Highly dependent on visibility and clear line of sight to the staff.
Topographic surveys for contour mapping.
Location surveys for roads, railways, and reservoirs in hilly regions.
| Feature | Multiplying Constant (K) | Additive Constant (C) |
|---|---|---|
Formula | K=if | C=f+d |
Standard Value (Ordinary) | 100 | 30 cm−45 cm (0.3 m−0.45 m) |
Value with Anallatic Lens | 100 | 0 |
Anallatic lens is an internal focusing convex lens placed between the objective glass and the eyepiece to make the additive constant zero.
Option A and Option B represent individual constants, but since both belong to a tacheometer, Option C is the correct answer.
C is correct — Both multiplying constant (K) and additive constant (C) are fundamental constants used in calculating distances with a tacheometer.
Always remember for exam questions: if an anallatic lens is present in the tacheometer, C=0 and K=100, simplifying the distance formula directly to D=100s.