This is a complete guide on how to correctly book levels taken using the height of collimation method. This is how all Site Engineers in the UK will record and work out their readings.
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.
Remember to check your Auto Level too, by doing a two peg test. There is a guide to doing a two peg test on this site.
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 for the Height of Collimation 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.
In the picture below, you can see the information captured in the header of the page and we have 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. Notice that I do not record a dot to separate the metre distance reading, I record the reading in millimetres as this saves time and confusion when measuring less than 1m on the E-Grad Staff. The second reading taken is 2489mm 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 1958mm 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 3045mm and is on a Fore Sight (point D) and is noted in the Fore Sight Column and D is noted in the Distance Column.
Moving the Auto Level to the next setup our first reading is a Back Sight to Point D. The reading of 1157mm 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 865mm 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 3754mm 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 2452 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 1965mm and is noted down in the Fore Sight Column and Datum B is recorded in the Distance Column.
This is all the readings we take for this levelling traverse and we can now work out the collimation and reduced levels for this run.
The first calculation we do, works out the height of collimation of the auto level, that is the height that you are viewing when you look through the instrument at the staff. This is done by adding the Back Sight reading to the reduced level of the point that the E-Grad Staff is being held on. In this example we have 2.596+105.545=108.141 and we write down the 108.141 in the Collimation column. Now that we know the height of the auto level we can move onto calculating the reduced levels of the other points we have readings for. The next calculation is for point B and we need to take away the Intermediate sight from the Collimation, so the calculation is 108.141-2.489=105.652 and this is written in the Reduced Level column.
We have a further two more calculations to do on this setup, we have one Intermediate Sight and one Fore Sight. The same method is used for these calculations, so we have 108.141-1.958=106.183 and this result is noted in the Reduced Level Column for Point C and then we have 108.141-3.045=105.096 which is noted in the Reduced Level Column for Point D. This is the last point calculation for this current setup.
As we have moved the auto level, we need to calculate the height of collimation for it again. This is done in the same way we did the very first calculation, in this case though we have 1.157+105.096=106.253 and the result is noted in the height of collimation column. Notice how we have not started afresh but using the same line. This has two benefits, first it saves space in the book and second it shows that these readings are all part of the same levelling traverse.
We now move onto the last reading of this setup which is the fore sight and calculate thus. 106.253-0.865=105.388 and note the result in the reduced level column.
As we have moved the auto level again, we need to calculate the height of collimation for it again. This is again done in the same way we did the very first calculation, in this case though we have 3.754+105.388=109.142 and the result is noted in the height of collimation column.
We have a further two more calculations to do on this setup, we have one Intermediate Sight and one Fore Sight. The same method is used for these calculations, but this time we have 109.142-2.452=106.690 and this result is noted in the Reduced Level Column for Point F and then we have 109.142-1.965=107.177 which is noted in the Reduced Level Column for Datum B. This is the last point calculation for this levelling traverse.
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.
I have been doing this kind of Levelling for years and over that time I have picked up some tips for being able to check Automatic (Dumpy) Levels quickly. They are all laid out on this site on the page quick and easy checks on automatic (dumpy) levels.
If you want a spreadsheet that works out the collimations and reduced levels for your levelling traverse then there is this survey level book spreadsheet for free from the Lichfield Survey Supplies website.
The book used in this example is the Chartwell 2426 Survey Book, these books are the all weather books used on nearly every construction site in the UK. Check out the latest prices for the Chartwell 2426 Height of Collimation books here.
Recommended Automatic Levels.
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Don’t forget to check out the latest price and availability of the Chartwell Height of Collimation book as used in this example.