Here's a posting on cache mode for the T2 from one of it designers, Dave Johnson:
"Cache mode" on most F75 and T2 versions is very similar to "Slow mode" on the F70. The response is slow, with improved sensitivity to large deep targets. However this means that the signals from shallow targets will smear, with a cost in both sensitivity and in ability to discriminate and ID targets. Shallow targets will do better in cache/slow mode if you slow down to a crawl, but the default and boost modes work better for the shallower stuff. And, if you really do want best response on deep stuff, all metals mode goes deeper than disc mode. For finding the deep stuff, an alternative to Cache/Slow mode is to search in Boost mode all metals, then switch to disc when you suspect you're fighting trash. ........Another way to deal with shallower stuff is to search in Cache/Slow mode with the searchcoil lofted several inches above the ground. This will result in a big cut in response to shallow trash, but perhaps more importantly it will achieve a large reduction in ground mineral interference (since ground itself is the shallowest target) and in mineralized ground will usually enable deeper detection than if you were scrubbing the surface in a misguided attempt to "get as close as possible to the deep targets".
Here's another from Keith Southern:
All metal does make it easier on the T2/F75 to size iron ..alot of iron on that series in Disc mode sounds like nails even though its larger than nails..Very compressed iron tone on those units...
One thing I like to do with a T2/F75 that has cache mode is to stay in Disc set it to zero 2F Tone and work through a dead site full of iron and listen for the larger iron hits Vs the shorter nail hits..you can do it in Cache mode its so slow to retune..
Just the other day I was in a nail pit and pulled out a Nice Iron Heel plate doing that..
Good digs..
Keith