NA2/NAK2-2.0.0en
Measuring
19
Project:
Height difference of very high
accuracy.
Use the GPM3 parallel
plate micrometer and
invar levelling staffs.
In sloping terrain, the
lower part of the staff
should not be used, as
refraction close to the ground
can cause errors.
In sunny weather an
umbrella should be used
to shelter the instrument to
ensure that the level is
protected from the glare of the
sun.
Precise levelling
Procedure:
1. Sequence of measurements
is the same as with line
levelling. However, the best
observing length is approx.
25m.
2. When reading the staff, turn
the micrometer knob until a
graduation line is centred
between the wedge-shaped
hairs of the reticle.
3. Centimetres are read from
the staff and millimetres from
the micrometer scale.
4. Leica invar staffs have two
sets of graduations. These
are read alternatively
between foresight and
backsight. This provides two
independent results and
serves as a check.
Example above:
Staff reading
=
77 cm
GPM3 reading =
0.556 cm
Height
=
77.556 cm
NA-43
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