What is Series Levelling?

Series Levelling can be described as the procedure of moving the instrument through a succession of points. At each level position a BS and FS is read and booked. See diagram at the lower right. details. This procedure becomes necessary when heights are needed at a number of points or the BM is some distance from the site of interest.

• Series levelling should commence and terminate on points of known RL (BMs).
  

Referring to the diagram on the lower right the field procedure is a follows:

1. The instrument is set up approximately 50m to 100m away from the BM (point A) and a staff reading to the nearest 0.001m is observed and booked. (picture of the staff)
2. The staff is moved to the FS position (point B) and again the observation is observed to 0.001m and booked. (example of the booking sheet)
• Care should be taken that the BS distance is equal or nearly equal to the FS distance.
• This point (A) is referred to as a change point and must be a firm physical object.
3. The level is then moved to point 2 approximately 50m to 100m from staff, as shown in the diagram above. A BS reading is then observed to the staff at B to the nearest 0.001m.
4. If any levels are required to objects in the immediate area of the level, then intermediate levels are taken and booked in the intermediate sight column.
5. The staff is then moved to the next change point (C) and a FS reading taken.
6. These steps are repeated until the end of the levelling run is reached - the last point (FS) should always be a point of known RL. When the observations are complete:-
7. The observations are then reduced as shown here. Steps at top right.

Series Reduction Steps

• Sum the BS Column and sum the FS column
• Sum of BS minus sum of FS should equal the first RL minus last RL
• Calculate the rise and fall for each line
• Sum the rise and fall columns. The difference between the two columns must equal the difference between BS and FS column.
• Using the rise or fall value for each line calculate the RL for each change point.
• Subtract the last RL from the first RL. The result should be the same as BS - FS