White’s Electronics TDI - Manual (Page 29)

PulseScan TDI Owner’s Guide 9
Therefore, on a low-conductive target (small to medium gold, nickel coins, and
small iron) the pitch of the audio tone might rise.
When the search coil goes over a high-conductive target (large gold, most silver
and copper coins and most large iron) the pitch of the audio tone might fall.
It might be noted that the low tone heard over large non-iron targets is usually
smoother than the low tone heard over iron targets which can be irregular. In
addition, flat iron or steel objects, such as tin lids and flat sided cans can give
a mixed response. This can sound like low tone, high tone, low tone as coil
passes over the target. The sweep will have to be slower to notice this. The
high-tone response is usually stronger and longer, but with time and practice this
can be helpful to identify flat iron.
With practice, you will be better able to use your low tone and high tone to help
you get an idea of what kind of target you are detecting and help to eliminate
some trash items. However, it is always better in a new area to dig everything
until you get an idea of what you are likely to find. Keep in mind that no system
is perfect, and when in doubt DIG!