Dave, I air test my detectors in my basement a lot, don't get the exact same results every time, sometimes have EMI problem. Today, no EMI, here is ID Edge results. Sens @9. 8" coil: Merc dime 9" with 80% diggable high tone. Other times I get max 8" on the dime with same tones, but never less than 8". Silver quarter 10" with diggable tones, other times 1/2" less. Also have the 10.5" coil made for the Edge, goes up to 1" deeper on the dime and quarter in air, but where it really shines is you don't need such a tight sweep overlap, maybe because the inner coil is oval shaped and it scans a larger area down deep. Another ID Edge user said his 10.5" coil doesn't give all those high tones on deep rusty nails, he thinks because it gets a better reading on deep nails than the 8" coil does. I used the 10.5" just 4 times so far and have not dug a nail yet, but maybe there were no nails where I used it. The 10.5" stays on the detector, I like it even tho it is heavier than the 8". I recently bought the 10.5" from Detector Electronics in Mass., phone No. is 508-460-6244, $122 shipped. Yesterday I was searching along the river where it floods every year, stuff is very deep there. Dug no old coins, but dug a 22 cal lead bullet at 5"- 6". I know if I pass the coil over old silver I will hear it.