Estimating Target Size And Depth - Fisher Labs F75 User Manual

SEARCH TECHNIQUES (continued)
Estimating Target SIZE, DEPTH, and SHAPE
When the trigger is pulled to activate Pinpoint, the LCD displays estimated depth. The
estimate is based on the presumption that it is a coin-sized target.
But what if it is not a coin-sized target? The most common example is that of an aluminum
can. Flattened aluminum cans are usually identified as zinc pennies or as dimes. Their
large size will produce a strong signal, tricking the microcomputer into thinking that it is a
shallow coin.
The following explains techniques for differentiating buried aluminum cans from coins.
Sweep back and forth to get a feel for the target, keeping the searchcoil close to the ground.
Now, continue to sweep back and forth as you slowly raise the searchcoil higher and
higher. If the response diminishes quickly and never gets very broad, the target is probably
a coin. If the response diminishes slowly as you lift the searchcoil, and you get a broad
response, the target is probably an aluminum can. If you practice this by laying a coin and
a flattened aluminum can on the ground, you will quickly understand how to differentiate
the two and you will probably never have to dig another aluminum can again. And, you
will know whether it was deep or shallow. This technique works well in the All Metal
modes, and to a lesser extent in Discrimination mode.
Objects which are ring-shaped, or flat and round like coins, tend to give a narrower, crisper
response than objects of similar size with irregular shapes. The easiest way to demonstrate
this is with an aluminum screwcap from a soda bottle. In its normal shape, it occupies a
volume, and gives a somewhat broader response than that of a coin. But if you flatten it,
the response will be crisper and more like that of a coin. Again, these differences are most
readily noticed in the All Metal modes.
Long skinny iron or steel objects such as nails usually produce a double response when
scanned lengthwise, and a weaker single response when scanned crossways. This is most
noticeable in the Motion All Metal mode. However, a coin lying on its edge can produce a
similar response, so rely on both the target ID as well as target feel to distinguish between
different kinds of objects. Objects within 2 to 3 inches of the searchcoil will often produce
multiple responses as you sweep across them, because the response field close to the
searchcoil is irregular.
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