is about correct. That suggested 2-second sweep time is more or less an industry recognized standard for the time required to sweep the coil <STRONG>one</STRONG> direction, from right-to-left, when covering a swath of about 4'. Then it would require about 2-seconds to sweep back the other direction, right-to-left, after advancing the coil for an efficient overlap.
This <EM>"2 feet per second"</EM> sweep rate has been an industry standard more or less forever. Thirty year old information published by Charles Garrett in his book suggesed that the sweep speed ought to be about 1' per second when starting out, but with experience that sweep rate should increase to about 2' per second. This was prior to the development of modern motion discriminators.
Also from earlier publications, we can read E.S. 'Rocky' LeGaye's suggestion that a left-to-right scan ought to typically cover about 2'-3', and that <EM>"1 foor per second is a fair average."</EM> Again, that suggestion, from his book printed in 1969, came about a half dozen years before we had ground cancelling discriminators. (aka 'motion discriminators')
Another source to find an answer is in "The Official Handbook of Metal Detectors" by Dr. Arnold Kortejarvi in which he also states that sweep speed should be about 1 ft. per second, unless the manufactuere's literature tells you otherwise. This was also from pre-VLF/Ground Cancelling circuitry days. Actually, this 1969 publication predates popular discrimination circuitry!
Most of these earlier publications had suggestions based upon the operator's manuals that were supplied with the various models they used in writing their books. To be a little more 'up-to-date,' let me refer to some operator's manuals that I have on hand.
Compass Scanner series: <EM>"Search at a slow, comfortable sweep speed."</EM>
Tesoro Toltec 100: <EM>"Swing the detector from side to side in about a three foot arc, ..... The Toltec was designd to get maximum depth without the frantic pace required by earlier motion detectors."</EM> These identical instructions are found in the manual for the Silver Sabre Plus, 'original' Bandido, Silver Sabre