Aquaculture Engineering (2+1)

Booking and Reducing Levels - Height of Instrument method

Unit 1- Surveying

Find out the elevation of points using different methods
Booking and Reducing Levels

Height of Instrument method

In this method, the height of the instrument (H.I) is calculated for each setting of the instrument by adding back sight (plus sight) to the elevation of the B.M. The elevation of (Reduced Level) the turning point is then calculated by subtracting fore sight from H.I the. For the next setting of the instrument the H.I. is obtained by adding the B.S taken on TP1 to its R.L.

The process continues till the R.L of the last point (fore sight) is obtained by subtracting the staff reading from height of the last setting of the instrument. If there are some intermediate points the R.L of those points is calculated by subtracting the intermediate sight (Minus sight) from the height of the instrument for that setting.

Check
The difference between the sum of back sight and sum of the fore sights should be equal to the difference between the last and first R.L.
∑B.S – ∑F.S = Last RL – First RL

1. The following staff readings were observed successively with a level, the instrument having been moved after, second, fifth and seventh readings.
0.865, 2.105, 1.025, 1.580, 1.865, 2.230, 2.835, 2.355, 1.760

Enter the above readings in a page of a level book and calculate the R.L of points, if the reading was taken with a staff held on a B.M. of 560.500

∑ B.S = 6.475 ∑ F.S = 8.565
Check = ∑ BS - ∑ FS = First R.L - Last R.L
= 6.475-8.565 = 560.500-558.41
2.09= 2.09