Personally, I only eyeball my doses whether it's freebase or changa. Thinking about numbers or weights leads to expectations pre-trip, imo, and that's the last thing you want. I find that with dmt, as acceptance is already key, just loading up your smoking/vaping device with a small, medium, or large dose is the least mentally involved (and distracting) method. You can always mediate your intake through your hits and the size of your inhales. I have one of the great, cheap ebay scales, but I only use it for measuring %yield and changa materials. When it comes to smoking, I just load it up and let it rip; that's been my method since day 1 and it's never let me down. Occasionally it can surprise you, but this is spice; when doesn't it?
peace
SB