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# How to Calculate the RL by HI method in surveying

## How to Calculate the RL by HI Method in Surveying.

In this article i will explain how to Calculate the RL by HI method in surveying, Let us consider an example as given below.

The leveling instrument was used to observe the subsequent readings.

0.450, 1.860, 2.755, 3.250, 3.675, 3.930, 0.885, 1.150, 1.945, 2.850, 3.635, 0.975, 1.950, & 2.585. The instrument was shifted after the Sixth and Eleventh readings. The elevation of  the first reading was 480.65m. Calculate the RL of all the points by using the Height of instrument method.

### Calculation.

As u can observe in the above drawing, the instrument is shifted after the Sixth and Eleventh reading.

So, first, seventh, and twelfth readings   👉 BS

Sixth, Eleventh, and 14th readings 👉  FS &

All of other remaining readings   👉  IS

### How To Convert the Bearings and Distances to Coordinates

👉 While Surveying, the first reading becomes BS and the last reading becomes FS.

Note:

• #### RL 👉 reduced level.

Now, let us prepare the Height of the instrument table from the above-mentioned data.

Following are the rules or formulas u should remember while calculating the RL in the height of the instrument method.

1 – HI = [RL + BS]

Whenever u get the BS reading, u have to calculate the height of the instrument in that particular change point. By adding the RL to the BS u will get the HI when u establish the instrument in the new change point.

2 – RL = [HI – IS or FS]

Once the height of the instrument is calculated, u have to deduct the IS & FS from the HI to calculate the RL of that particular station. This procedure should be continued until u get the new HI at the change point.

6. #### Sixth RL = [1st HI – First FS] = [481.10 – 3.930]         = 477.170

As u can observe in the below-given table, the IS And FS is deducted from the same HI until u shift the instrument & note down the new BS reading.

### Types Of Curves In Surveying Work

Once u note down the BS reading for the change point, again u have to calculate the HI And by adding RL to the BS.

5. #### 10th RL = [2nd HI – Second FS] = [478.055 – 3.635] = 474.420

Again calculate HI for the 3rd BS

3. #### Twelfth RL = [3rd HI – Third FS] = [475.395 – 2.585] = 472.810

All the calculated values should be entered as shown in the below-given table.

#### Remark

1 0.450      481.10 480.650 BM
2   1.860     479.240
3   2.755     478.345
4 3.250   477.850
5   3.675   477.425
6  0.885  3.930 478.055 477.170 CP1
7  1.150 476.905
8   1.945   476.110
9    2.850   475.205
10 0.975 3.635 475.395 474.420 CP2
11 1.950 473.445
12 2.585 472.810
Total Ʃ 2.310   10.150

### Arithmetic check

[∑FS – ∑BS]  = [First RL – last RL] [∑FS – ∑BS] = [ 10.150 – 2.310] = 7.840

[First RL – last RL] = [ 480.650 – 472.810] = 7.840

Hence, the calculation is the correct.