You answered part of the question right there 100hrs is nothing really when it comes to knowing/understanding a machine. Its like anything one has to put in the time to become efficient in the sport/hobby/or what ever one is trying to do. Example of what I can expect from buying a new machine even after 45+ yrs of playing the dirt digging crap. I think 1000 hrs down the road of digging gets me close in knowing the machine to a point of some confidence. Numbers on the screen lie most times as so many factors come into play for a signal and sound will be your best friend.
I went out this past Sunday, dug for 4 hrs and I had nothing in the pouch(even after emptying it 4 times) to even do a post, not that I didn't dig things it was mostly iron, or bits of aluminum, brass sheeting, and a few items that were ok.
The thing is I don't go out seeking the killer find, I go out to dig and in that process I guess (and wish) what the next target is before I dig. I don't think of anything, I forget about life, and all responsibilities when I go detecting. It's my time to unwind, dream of maybe just maybe it'll be a keeper. Then the unexpected happens I turn the sod and there it lays a round disk, made of copper, and sometimes silver, a cool piece of history, even a button, and it all comes up flooding the senses a keeper.
The main thing is not to get frustrated, enjoy, and when you get a little bummed out go hang it up for the day, and dream of another day to hunt.