- Set up the telescope at the first setup and focus and centre the stadia lines on the staff bubble is central.
- Set the height of the staff on a point with a known reduced level the bottom of the staff (B.S.) or above the H.I. (reduced level of the instrument) if the staff is fixed by the level line
- Read all the staff readings that are cut by all three stadia lines (top middle and bottom) of the vertical circle i.e. three staff readings.
Staff Readings of Dumpy Level For Leveling
The staff readings are generally taken when the vertical crosshair of the telescope cuts the staff. To read the staff, the following procedure is adopted.
- Stand exactly behind the staff and note down the staff intercept to the nearest mm, by estimating half mm at the graduation point where vertical crosshair cuts it as a. When the staff readings are required to the nearest cm only, then they can be read directly without estimation.
- Note the reading, to the nearest mm of intercept between the middle horizontal crosshair and staff graduation cut by it as b.
- Repeat the above steps for the staff readings corresponding to the lowest staff graduation line cut by the lowest horizontal crosshair.
Formula To Calculate Collimation Error: C = [(a - b) - k]*100, where
C = Collimation error in mm,
a = Upper staff reading,
b = middle staff reading,
k = Stadia constant which is 100 for dumpy level