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Muvable hair method can also be known as __________
Fixed hair method
Subtense method
Tangential method
both B and C
Subtense method
In tacheometric surveying, the movable hair method is also known as the subtense method. In this method, the distance between the stadia hairs is variable and can be adjusted, while the staff intercept remains constant by using a target staff of fixed length.
In tacheometric surveying, the movable hair method is also known as the subtense method. In this method, the distance between the stadia hairs is variable and can be adjusted, while the staff intercept remains constant by using a target staff of fixed length.
D=ifтАЛтЛЕS+(f+c) тАФ Horizontal distance equation in subtense method
i=nтЛЕp тАФ Stadia interval measured via micrometer turns (n) and pitch (p)
The stadia wire interval is adjusted using a micrometer screw until the target vanes on a staff of fixed length (staff intercept S) are bisected. The horizontal distance is then determined using the measured variable wire interval i alongside the tacheometric constants.
In the subtense (movable hair) method, the staff intercept S is kept constant while the hair interval i varies.
A micrometer screw is used to measure the variable distance between stadia hairs accurately.
In contrast, the fixed hair method keeps the hair interval i constant while the staff intercept S varies.
Useful for measuring long distances where reading a standard staff intercept directly is difficult.
Eliminates errors caused by optical refractions over variable staff lengths since a fixed target intercept is used.
Slower and more tedious field operation due to micrometer adjustment requirements.
Requires high precision in micrometer calibration to avoid measurement errors.
Tacheometric surveying in rough or hilly terrains.
Subtense bar measurements for precise horizontal distance determination without direct chaining.
| Feature | Fixed Hair Method | Subtense (Movable Hair) Method |
|---|---|---|
Stadia Hair Interval (i) | Constant | Variable (Adjustable) |
Staff Intercept (S) | Variable | Constant |
Measurement Tool | Standard Levelling Staff | Target Staff / Subtense Bar & Micrometer |
Tangential method (Option C) does not use stadia hairs at all; horizontal distances and elevations are computed using vertical angle measurements taken to two targets on a staff.
Option A is incorrect because the fixed hair method maintains a constant wire interval, whereas the movable hair method varies it.
B is correct тАФ Movable hair method is alternative terminology for the subtense method in tacheometric surveying.
Remember: Fixed Hair тЖТ Constant i, Variable S; Movable Hair (Subtense) тЖТ Variable i, Constant S; Tangential тЖТ No stadia hairs used.