Taking a reading on an E-Grad staff precisely and accurately is only the first part of completing a successful levelling run or traverse. It is important that your E-Grad staff readings are noted down accurately and in the correct format in a field book. This will enable you, and anyone else, to check your levelling work. There are two common methods for booking levels in a field book, and these are:-
- The height of Collimation Method
- The Rise and Fall Method
Both methods of booking the readings of a levelling run are the same. That is, the first reading of any setup is a Back Sight and would be booked in the column labelled Back Sight. The final reading taken on any setup is a Fore Sight and would be booked in the column labelled Fore Sight. Any readings taken between the first and last readings on any setup would be an Intermediate Sight and would be booked in the column labelled Intermediate.
Using the example from the post How to carry out a levelling traverse or run we would complete the field book in the following manner using the Rise and Fall Surveying Method.
The first part of the booking process is to complete the heading of the page. It is important that the date is recorded (you may wish to record the time also). Record what the levelling run is for, in this case it is for Station Control. And record your starting position and where you intend to finish the levelling run. For the example below we have used a spreadsheet version instead of a Chartwell Survey Level Book. The spreadsheet is available from Lichfield Surveys Supplies Ltd.
In the picture below, you can see the information we have captured and have noted the readings of the first leg of the levelling traverse. On starting the levelling traverse, we would note down the Reduced Level and the Station ID that we will start from. In this example I have noted down the Reduced Level as 105.545 and in the Distance Column I have noted Datum A. (Depending on the information you need, you may insert the distance read to the staff in this column, but I use the remarks column for further information like working out top of kerb levels.) Our first reading taken is our Back Sight, this is 2.596m, and is noted in the Back Sight column of the book. The second reading taken is 2.489m and is on an Intermediate Sight (point B) and is noted in the Intermediate Column and B is noted in the Distance Column. The third reading taken is 1.958m and is on an Intermediate Sight (point C) and is noted in the Intermediate Column and C is noted in the Distance Column. The forth (and last taken on this setup) reading is 3.045m and is on a Fore Sight (point D) and is noted in the Fore Sight Column and D is noted in the Distance Column. For this post I have used the Rise and Fall Spreadsheet courtesy of Lichfield Survey Supplies Ltd so the figures are worked out as I am entering them.
Moving the Auto Level to the next setup our first reading is a Back Sight to Point D. The reading of 1.157m is noted in the Back Sight Column. Note, that this is done on the same line as the Fore Sight Reading taken in the previous setup. The second reading on this setup is the last one, so is a Fore Sight and the reading of 0.865m is entered is entered in the Fore Sight Column and E is entered in the Distance Column, as we are reading Point E.
We now move the Auto Level to our last setup for this levelling run. Our first reading to Point E of 3.754m is recorded in the Back Sight Column on the same line as the Fore Sight Reading taken in the previous setup. Our next reading is Point F, which is an intermediate reading of 2.452m and is noted in the Intermediate Column and F is entered into the Distance Column. Our last reading for this levelling traverse is on Datum B which is 1.965m and is noted down in the Fore Sight Column and Datum B is recorded in the Distance Column.
This is all of the readings we take for this levelling traverse and we can now work out the rise and fall, and then the reduced levels for this run.
With the rise and fall method of booking a levelling traverse or run we need to first compare the relative readings we have just taken. We need to establish whether the base of the E-Grad staff has risen or fallen in height between two different readings. We have to remember that a lower number on a subsequent reading on the E-Grad staff means that the base of the E-Grad Staff has (Rise) risen, and similarly a greater number on a subsequent reading on the E-Grad staff means that the base of the E-Grad Staff has (Fall) fallen. In our example we have the Intermediate Sight (2.489m) less than the Back Sight (2.596m), this is a rise of 0.107m which is noted in the Rise Column. The rise of 0.107m is then added to the reduced level from Datum A (105.545+0.107) to give 105.652m as a reduced level for Point B.
We have a further two more calculations to do on this setup, we have one more Intermediate Sight and one Fore Sight. We follow the same process as before, where we need to determine whether we have a rise or fall between the readings. For the next Intermediate Sight we again have a lower reading on the E-Grad Staff which means a figure needs to entered in the rise column again. This is (2.489-1.958) 0.531m and this is then added to the previous reduced level giving (105.652+0.531) a reduced level of 106.183 for Point C. The last point on this setup is Point D, for which we have a Fore Sight of 3.045m. This reading on the E-Grad Staff is greater than that of the previous Point C reading (1.958m) and thus would be recorded (3.045-1.958) in the fall column as 1.087. This would give a reduced level of Point D as (106.183-1.087) 105.096m.
Once the Auto Level has been moved and setup again we need to take the first E-Grad staff reading (of the setup) and note this in the Back Sight Column, in this case the figure of 1.157m is noted down for Point D.
This time we do not have to work anything out, it is purely a reference for the next calculation. We then have a Fore Sight reading of 0.865m for Point E. Once again, we have a lower reading on the E-Grad Staff which means a figure needs to entered in the rise column, but this time we have (1.157-0.865) 0.292m which when added to the previous reduced level (105.096) to give 105.388m for Point E.
Once the Auto Level has been moved and setup again we need to take the first E-Grad staff reading (of the setup) and note this in the Back Sight Column, in this case the figure of 3.754m is noted down for Point E. Again, we do not have to work anything out, it is purely a reference for the next calculation.
We have a further two more calculations to do on this setup, we have one more Intermediate Sight and one Fore Sight. We follow the same process as before, where we need to determine whether we have a rise or fall between the readings. For the next Intermediate Sight we again have a lower reading on the E-Grad Staff which means a figure needs to entered in the rise column again. This is (3.754-2.452) 1.302m and this is then added to the previous reduced level giving (105.388+1.302) a reduced level of 106.690m for Point F. The last point on this levelling traverse is Datum B, for which we have a Fore Sight of 1.965m. This reading on the E-Grad Staff is again lower than that of the previous Point F reading (2.452m) and thus would be recorded (2.452-1.965) in the rise column as 0.487. This would give a reduced level of Datum B as (106.690+0.487) 107.177m.
At this point it would be best practice to compare our calculated level for Datum B with the known value for Datum B to ensure that the levelling traverse has been done successfully. If we didn’t know what the reduced level for Datum B was beforehand then we would need close the traverse by going back to Datum A.
The advantage of using the rise and fall method of booking is the easy checking for potential errors in the Back Sight and Fore Sight readings. These checks are highlighted in yellow on the spreadsheet and are calculated automatically for you
If you want the spreadsheet used in this example then it can be found at Lichfield Survey Supplies Website. The LSSL Rise and Fall Level Book Spreadsheet that works out the rise, fall and reduced levels for your levelling traverse automatically from your Back Sights, Intermediate Sights and Fore Sights.
Recommended Automatic Levels.
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Don’t forget to check out the price and availability of the rise and fall level book.