I've dug up only two of those (one direction tones). Both turned out to be a coin. One was a wheaty standing and one was a buffalo Nickle.... Both standing upright. I couldn't tell ya why it only pinged a single from one direction though.
hey Chris , this little beauty was about 9 inches deep and when i went over it , it sounded like a nail . deep broken low chirp target then i hit it at 90 degrees (as i always do to these type of sounding targets ) and it sang very sweet and knew it was something good . it was standing on edge so the profile was minute one way being so deep made it resemble a deep nail bit in tone but comming back the other way i hit the flat round side which is much larger and i was thinking it could be a coin by its nice sounding tone . because it was standing on edge and its location (on the edge of a nice slope with great drainage) both sides are in beautiful shape .
I usually check the numbers to determine whether or not to dig one way hits. 99% of the time, it's a nail. Last month, though, I got a nice one-way hit and dug up my oldest coin, a half Real. If it weren't for the high numbers, I don't know if I'd have dug it.
My standards are much lower. Just the hint of a nice sounding tone in any direction and that target will see the light of day That's especially true if the cellar hole site I am at hasn't given up a copper in a while lol