Precise leveling is a crucial aspect of surveying, and calculating the back sight is an essential component of this process. Surprisingly, back sight calculations are not as daunting as they may initially seem and can be effortlessly mastered by following the appropriate steps. The back sight is the measurement from the benchmark or previously established elevation to the instrument. Understanding how to calculate the back sight empowers surveyors with the ability to determine the height of unknown points with remarkable accuracy.
To initiate the back sight calculation, you will require specific data, including the benchmark elevation, the instrument height, and the rod reading. The benchmark elevation is the known elevation of the starting point, while the instrument height is the height of the surveying instrument from the ground. The rod reading is the measurement taken from the bottom of the rod to the target point being surveyed. With this information in hand, you can proceed to calculate the back sight using the formula: Back Sight = Benchmark Elevation + Instrument Height + Rod Reading.
For instance, consider a scenario where you are surveying a point with a benchmark elevation of 100.00 feet, an instrument height of 4.50 feet, and a rod reading of 2.75 feet. Plugging these values into the formula, we get: Back Sight = 100.00 feet + 4.50 feet + 2.75 feet = 107.25 feet. This calculated back sight value serves as the foundation for subsequent elevation determinations in the leveling process. Mastering the art of back sight calculation not only enhances your surveying skills but also ensures the accuracy of your leveling results.
How to Calculate Back Sight
A back sight (BS) is the final measurement taken before moving the level and rod to a new location. It is used to determine the elevation of the instrument and is necessary for calculating the elevation of the next point.
To calculate the back sight, follow these steps:
- Measure the height of the instrument (HI) using a level rod.
- Subtract the reading of the rod at the bench mark (BM) from the HI.
The formula for calculating the back sight is:
Back Sight (BS) = HI - BM
For example, if the HI is 1.250 m and the BM reading is 0.375 m, the back sight would be:
BS = 1.250 m - 0.375 m = 0.875 m
People Also Ask About How To Calculate Back Sight
What is a back sight used for?
A back sight is used to determine the elevation of the instrument and is necessary for calculating the elevation of the next point.
How do I calculate the HI?
To calculate the HI, add the height of the instrument (mounted on a tripod) to the elevation of the bench mark.
Can I use a different benchmark to calculate the back sight?
Yes, as long as the elevation of the new benchmark is known. Simply subtract the reading of the rod at the new benchmark from the HI.
