There used to be more obvious differences between the Fast Motion (4-filter type) and Slow Motion (2-filter type) motion discriminators.
In technical consideration it is a difference in what they refer to as "ring time."
The earliest motion discriminators, designed by Bounty Hunter, were the Red Barons and they used an almost 'rocket speed' sweep requirement. Eventually, White's models, licensed by Bounty Hunter to use their patented motion discrimination (4128803), were developed that set the standard by which most 4-filter & 2-filter designs were compared. These were the 5000 and 6000 series units. In time, they evolved into models that used White's own technology and not the BH patent, and the refined versions we have today in the XL Pro and XLT, for example, while still 4-filter designs, are really considered more of a slower-to-moderate sweep speed design.
While other makes and models have been produced using a 2-filter, slow-motion circuitry, perhaps all of them have to be compared to the Tesoro line of detectors. I feel Tesoro really set the standard by which all other 2-filter designs are compared. The Tesoro design can be considered slow-motion, and in some cases even ultra-slow capable.
As such, the Tesoro motion discriminators are <EM>"Slow-Sweep"</EM> designs. They do not require the ultra-slow sweep of the Explorer and are a little more forgiving if you use a faster (moderate) sweep speed.
In more mineralized ground, however, the 4-filter designs can be swept a little faster and sometimes need it for improved performance. On the other hand, the slow-motion 2-filter discriminators require a slower-motion in the more mineralized environments. A too fast sweep can greatly impact the detector's performance ... negatively. <img src="/metal/html/frown.gif" border=0 width=15 height=15 alt="

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Now, while the Tej