One of the most important factors in serchcoil depth is the size of the coil. While the mathematical calculations to determine the total area of an elliptical coil are complex, the final answer is almost exactly the same as the area of a circle whose diameter is half the total of the length/width of the elliptical coil. In other words, for the Mini DD, the length (6.75") plus the width (3.5") total 10.25", and half of that is 5.12". Therefore, the area of the Mini DD is about the same as a 5.12" diameter round coil. However, the reason why all major detector manufacturers "stretch" (elongate) DD coils is that by doing so they 1) increase ground coverage and 2) slightly increase depth, by 8-12%. THUS.... the Mini DD really has the depth of (about) a 5.5" round DD. It has been reported that the 5" Excellerator actually measures 4.75"; if so, that would explain why almost all persons who have tested the two claim slightly greater depth from the Mini DD. Another advantage is, again, ground coverage; the Mini DD cuts a "swath" 6.75" wide, whereas the 5" excellerator cuts one 4.75" wide. Personally, I feel that the 6X4 Mini DD is absolutely the best "accessory" coil for the MXT, although MOST owners of it will use it as their #1 coil. Keep up the good work; HH Jim
