Transferring Datums. Temporary Bench Mark (TBM). Temporary Bench Mark (TBM) from which levels are taken. A Temporary Bench Mark (TBM) is a known height point from which all levels are taken. The TBM can be related to an Ordnance Survey Bench Mark. . The TBM can be surrounded by concrete
Temporary Bench Mark (TBM)
Temporary Bench Mark
(TBM) from which levels are taken
A Temporary Bench Mark (TBM)
is a known height point from which
all levels are taken.
The TBM can be related to an
Ordnance Survey Bench Mark.
The TBM can be surrounded by concrete
and a timber enclosure for protection.
Ordnance Survey Bench Mark
Level taken from here
Ordnance Survey Bench Mark – datum which marks the height above mean sea level at Newlyn in Cornwall.
These datum's are established by the
Government Survey Office and are
usually permanently marked on public
building, bridges etc.
Example of Ordnance Survey Bench Mark
A Datum peg is a level point that is established in relation to a
Temporary Bench Mark.
The datum is a level reference point for the building activities, a few are shown
Datum peg at
Using Straight Edge and Level
Mark the position of the level
on the straight edge to ensure
it remains in the same
Drive a peg (X) in the lengths of the straight
away from the datum and level.
To maintain accuracy the spirit level
and straight edge should be reversed at each intermediate
leveling point as seen point B on the straight edge remains on peg X and
A swings round to peg Y.
Any inaccuracies in the level and straight edge are corrected by reversal
of the level and straight edge as illustrated below.