Mike, pretty much same thoughts here with when to dig...i am like you and although ive been detecting for a very long time, it was a new ball game since i got my at pro last xmas...learning curve! For one, i wasn't used to a dd coil, pinpointings a little diff. Than the years with concentric coils..but im getting better at that......with whats already been said as for digging...i just simply dug bout anything that repeated , or stays close to any certain numbers....just to see "what the heck is that???lol!
I did run into a few of those "90" n above signals few times too...only to find a large iron target. Or like in my front yard ...one that i have yet to find...
Kind of a "fooled ya" signal ....in the 90's....small pin point. (Until i raise the standard 8.x11dd coil im using ...)and can still get a pin point ten inches above the ground.....so probably a laaaarge iron target more than a foot down...
Those #30's thru #40 you mention.....well, since i do NOT want to miss any sort of ring...unfotunatly...i dig them anyway....just incase
Most of the.time it is a ball of alum. Foil or smthing similar....some of those pesky lil alum siding "trimmings" from an alum. Sided house (like mine, of curse...or of course!!) been falling in the #40 to #45 range....again i dont want to miss any rings or gold ....so i dig ....dig .....dig.....and dig some more...
So you seem to be thinking and doing the right thing....just dig all those numbers,like myself, and if you think twice about it...just dig it!
On a last note...about doubting a signal
Couple months ago.......i was a a local park...not really finding much...few older wheats ..n new coins...and those #:$@"!#_ zincolins...
That. USUALLY give # somewhere in between a 65 to a 69,maybe 70 ish.....at two inches deep...
Was getting kinda burnt on digging them....and i had yet another signal just like that 8 feet from a side walk in the park and 15 feet from my truck....n i thought......man.....another zincolin.........walked away from it....stopped....went back to it...
.....Alright....Ill dig the thing.........yeah.....it turned out to be an 1867 TWO CENT PIECE!!
Just some food for thought... HH........keep digging!!