Combinations - Combining mdma with excipient

[Absu]

Hey guys, swim is doing a paper in college about meth labs and drug production in the country, getting in a little on the possible compliance by legal chemical labs in large production operations, and swim came around this question and he doesnt seem to find the answer anywhere, when people are going to make the "mix" for a pill, 3 substances for example, how do they manage to completely mix them in a way that they know is accurate? like 33%33%33%?
or 20%50%30% swiy knows what i mean... is this done with a machine? or just putting the 3 predetermined amounts of powder together and shaking it thoroughly is enough? seems like it would be very accurate but a machine doing the job would do that same thing, just shake.. no?
I hope swiy can give swim some input on this.