Been a busy day. Went for a hike with my youngest son, doing a lot of plant photography, then fed some horses, then headed home to do a bunch more coil testing. Here are the results below. The largest coil got the best depth of the two, however, the 5" x 8" wins the depth overall using the tiny nugget flake. It won by 1/2" with a reading of 2.5". Throw in some mineralization, and the large concentric coil will start to fail. I think Garrett really researched coils when designing this new gold metal detector.
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