Survey Methods
Field Measurements

In these notes we look at the procedures to be used in order to perform a level traverse or level run, the purpose of which is to determine the difference in height between points a long way apart or with a change in height greater than the length of the level staff.

Reduced Level (R.L.)
The height of a point above the selected datum.

Mean Sea Level (M.S.L.)
This is the datum most frequently used. Datum for Australia is the Australian Height Datum (A.H.D.)

Backsight (B.S.)
The first reading taken by an observer at every instrument station.

Foresight (F.S.)
The last reading taken at an instrument station

Intermediate sight (I.S.)
Any reading taken at an instrument station which is NOT a permanent stable reference point.

Bench Mark (B.M.)
A point of known Reduced Level (R.L.). Usually a permanent stable refernce point.

Temporary Bench Mark (T.B.M.)
Where only realtive heights are required or a bench mark is required within area of work T.B.M. is established.

Change Point
The point at which the position of the instrument is changed, making it both a backsight and foresight.