I found this information on a tech support website for the BigFoot coil. Hope it helps you out.
"The Bigfoot coil is a completely new concept in coil design. It is not shaped differently JUST to LOOK high tech ..... IT IS HIGH TECH! This particular shape is necessary to house a coil design known as differential geometry. This design has two goals. First to cancel the effect of much of the ground mineralization before it gets to the detector and secondly to cover a large area of ground in one sweep from tip to tip for the full 18 inches of the coil length, much like a windshield wiper. An added bonus is that it helps to reduce 60 cycle interference, such as transformers and power lines.The BIGFOOT is 18 inches long and 3 1/2 inches wide. This model is especially designed to work on White's Model DFX.
It will, however, work on the New MXT as well, but in a unique fashion. The Bigfoot on the MXT will produce a single beep on the front half of the coil and either a double beep or a wide beep on the rear half of the coil when passing over a target. In adddition it may read 2 numbers higher on certain targets, which can skew the icons (e.g.quarter to read half-dollar). Even though the MXT tracks the ground automatically while searchng, do not forget to ground balance initially by pushing the coil up and down a couple of times with the tip of the coil on the ground at a 45 degree angle as noted in the last paragraph below, with Track toggle set to GND. After that you can either leave tracking on or set toggle to LOCK. I prefer to lock tracking off except in heavy mineralization.
While the detector is operating in GEB DISC(motion mode) the BIGFOOT is detecting targets across the full 18 inches of coil. When the detector is operating in GEB all metal (non-motion mode) the BIGFOOT is detecting targets ONLY on the front half of the coil. Unlike the XLT, the DFX does NOT require the use of"Absolute Value" as the DFX only detects on the front half in the all metal mode, such as when in the Prospecting Mode.
Pinpointing with the BIGFOOT is very simple and accurate. Squeezing the pinpoint trigger on the detector will make the BIGFOOT go blank (negative) on the back half (9 inches) of the coil. The front half of the BIGFOOT remains sensitive (positive). In other words, the target will only be heard under the front half of the coil. The trick, then, is to center the target by moving the coil from side to side till is seems to be midway from either edge and then squeeze the pinpoint trigger and push the coil forward like on a shuffleboard. The target will disappear as it leaves the midsection of the coil (marked by the two arrows) Thus by pushing the coil forward and backward you can easily hear the sound of the target appear ( when it is under the front part of the coil ) and disappear ( when it is under the rear half of the coil) That point where it appears and disappears is exactly at the center of the coil between the arrows. The rear half of the coil is actually rejecting the target and so you hear a very distinct sound when the coil is pushed forward and the front half leaves the target. "
