Fisher Labs F 75 User Manual page 15

Ground Balancing (continued)
MANUAL GROUND BALANCING
In most situations, it is preferable to push the trigger switch to activate FASTGRAB automatic
ground balancing. Generally, it is best to first let the computer automatically cancel
interference from ground minerals. However, for gold prospecting, searching on a wet
saltwater beach, or searching in an area with so much metal trash that there is no clean
ground for the computer to sample, we recommended that you manually ground balance.
Manual ground balancing requires a bit of skill, acquired with some practice.
The range of ground balance settings indicated on the display range from 0 to 99; however,
each displayed number spans 5 detent steps on the settings knob. The actual internal ground
balance settings change with each step; there are a total of 500 different settings. Under some
ground conditions you may be able to hear the individual steps in the setting.
The Fe O bar graph on the LCD display indicates the amount of magnetic mineralization. The
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searchcoil must be in motion to measure Fe
by pumping the searchcoil, as in the Ground Balancing procedure.
The two-digit G.B. Setting number displayed on the LCD indicates the type of ground
mineralization.
Some typical ground mineralization types are:
0 – 10 Wet salt and alkali
5 – 25 Metallic iron. Very few soils in this range. You are probably over metal.
26–39 Very few soils in this range -- occasionally some saltwater beaches
40–75 Red, yellow, and brown iron-bearing clay minerals
75–95 Magnetite and other black iron minerals
When manually ground balancing, try to "feel out" a spot on the ground to make sure there is
no metal present. In order to avoid locking onto metal, the computer will not balance to
ground where the GB setting is less than 40. Where the ground reads less than 40, manual
ground balancing is required.
To perform the Manual Ground Balancing
operation, do the following:
1. Select the MANUAL G.B. function
The legend G.B. SETTING appears.
The present ground balance setting
is displayed (0-99).
The message PUMP COIL TO G.B.
will appear.
2. Physically pump the searchcoil and
detector up and down over the
ground.
Lift it about 6 inches above the
ground and lower it to within 1 inch
of the ground, about once or twice a
second.
Comprehensive Operating Manual & Guide to Metal Detecting
O . The most accurate measurement is obtained
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F75
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