Fix the aluminum base plate with bubble firmly on the ground
where the measurement is going to be taken. Try to center the
bubble. Use the extra level provided, to achieve maximum
horizontality of the base plate.
Remove the gravity meter from its case with extreme care.
Dropping the gravity meter would cause irrepairable damage and we
will not have a gravity profile. This will result in having a
type of final exam which nobody wants. Please DON'T BE A NERD.
Put the gravity meter on the base plate.
Put the batteries into the holes on top of the instrument.
Turn the shiny metal piece in the direction shown by the arrow
in Fig. 1, to cover the (+) poles of the batteries. This action
will engage the batteries.
Turn the black knob ( ``a'' in Fig. 1) so that the lower ring
``b'') touches the bottom ring of the concentric cylinders ( ``c'' ).
Observe that the levels are lighted.
Level the instrument by rotating the knobs at the bottom.
Rotate two of the three knobs simultaneously and check the levels.
When both bubbles are at the centers of their respective levels,
the instrument is leveled.
Look through the eyepiece ( ``d'' ). What you should see is
``before'' in Fig. 2. ``Before'' meaning before turning the knob with
numbers.
Turn the knob with numbers and observe the movement of the
lighted strip between two dark strips towards the center. Continue
turning the knob slowly till the transverse line intersecting the
cross hairs is in the middle of the lighted strip ( ``After'' in Fig.
2 ). If the strips do not move towards the center, gently tap the
top of the gravity meter. (If tapping does not work, pull off the cap
to the right of ``d'' and the numbered knob in Fig. 1, and adjust the instrument
range with a screwdriver. Only do this at the start of a survey.)
Read the value in instrument units. The horizontal lines on
the cylinderical surface of the knob are hundreds. The numbers on
the knob are tens and the vertical lines on the cylinderical
surface are ones. Use the vernier scale for the value after the
decimal point.
Record the time, elevation, station number and the instrument
reading. Re-level, re-center, and re-read the instrument at least three
times for each measurement station.
Move to the next station and repeat all the preceding steps.
Fig. 1: top plate and controls of the Worden gravimeter.
Fig. 2: views through the eyepiece of the Worden gravimeter.
