Measurement Instrument: Subtense Bar

Subtense bar is an important measurement instrument used in surveying for measuring horizontal distances in undulated areas. It is a simple and compact instrument that consists of two vertical staves, a horizontal bar, and a target.

How Does Subtense Bar Work?

Subtense bar works on the principle of subtense. In this method, a baseline of known length is established between two points, and the distance between any two points is measured by subtending an angle from the two ends of the baseline. The subtense angle is the angle subtended at the two ends of the baseline by a rod or a target held at the point whose distance is to be determined.

Advantages of Subtense Bar

Subtense bar has several advantages over other measurement instruments, including:

1. It is a simple and compact instrument that is easy to handle and transport.

2. It can measure distances accurately in undulated areas, where other instruments like a chain or tape may not be suitable.

3. It is less affected by temperature and tension, which makes it more reliable than other instruments.

4. It can be used to measure both small and large distances.

Limitations of Subtense Bar

Subtense bar also has some limitations, including:

1. It requires two people to operate the instrument, one to hold the target and the other to read the measurement.

2. It is only suitable for measuring horizontal distances, and cannot be used for vertical or inclined distances.

3. It is affected by atmospheric conditions like fog, haze, and heat waves, which can cause errors in measurement.

Conclusion

In conclusion, subtense bar is an important measurement instrument used in surveying for measuring horizontal distances in undulated areas. It is a simple and compact instrument that is easy to handle and transport, and can measure distances accurately in a variety of conditions. However, it also has some limitations that must be taken into account when using the instrument.

The subtense bar is an instrument used for measuring horizontal distances in the areas where direct changing becomes difficult due the undulation.