Personally I work different than most people here...
I've worked with mg scale, and also just with 0.01g (or 10mg) scale, or also with no scale at all.
I have worked with measuring accurately every single dose I smoked, but I have also often worked differently. I often have loaded anyways more than one dose in my GVG at a time, like maybe two doses or so (say, 0.06g), and then I just vaporize till I can't, till I don't even know how to operate the lighter anymore. I do this only when I'm aiming for a breakthrough, of course. Sometimes this is in one hit, sometimes in three, it depends....
Or if I don't want a breakthrough, I just take small hits and get to where I want.
The thing is, I already know before the trip starts, as soon as I take the hit, by the initial effects when im holding the vapor in my lungs before the real effects come up, how far i'm gonna go, so I can 'callibrate' myself pretty well and know if I should vaporize more or not.
I'm not saying you should do this, or recommending to beginners, I'm just sharing my own experience. Maybe it's better you get a milligram scale because it might be useful for DMT or extremely important for other substances (such as 5-MeO-DMT), and then with DMT once you know your own dosage more or less and you feel confident to smoke it without a scale, you can do it. But maybe better get some experience before that.
As for pharma, personally I need a very high dose of DMT for pharma, like 200mg, so a mg scale really is not necessary, a 10mg scale would be more than enough. The difference of +-10mg would be imperceptible for me with pharma. There's this weird aspect about pharma that a very high dosage is needed by some people, but when taking full-plant brew like ayahuasca, I and others do not need such high dosages as compared to other people. Must be somehow related to other plant components that change metabolism of DMT.