^^ Use gel caps!
Calibrate your scale and test it with a calibration weight until you are content with the accuracy.
Weigh out a gel cap numerous times until you notice a consistent reading. If the gel cap weighs differently every time you weigh it, then weigh the gel cap numerous times and calculate the average.
Note the average weight of the gel cap.
If the numerous weights of the gel read between .089-.091 then the average and most probably accurate weight of the gel is .090.
If the numerous weights are drastically different than calculate each reading.
Example
1st reading = .091
2nd .088
3rd .090
4th .092
5th .091
6th .089
7th .093
8th .090
9th .088
10 .091
Add all the readings and divide by 10 and you have the average of 0.903, or for simplicity sake 0.090
If you want 5 mg of material than use a straw cut diagonally at the end into a scoop to scoop what looks like 5 mg into the gel cap and weigh it.
Weigh the gel a few times until you notice a consistent average reading. Again, if the readings are drastically different one after the other, than weigh out the gel 10 times, add all the readings and divide them to get the average.
If the gel cap consistently reads around .98 then you've added too much material and you must remove a bit of material and re-weigh it.
After removing a bit of material and re-weighing the gel cap, if it consistently weighs around .094-.096 then you have an average of most likely .005 of material.
Proceed to place in pipe and smoke!
This is about as easy to follow so there are no excuses for overdoses!
Hardly pin-point, but if your scale gives different readings consecutively for the same item, the closest to accurate you are going to get is by just weighing the gel numerous times, calculate the average and then once you've scooped some material into the gel, weigh the gel cap numerous times until what the scale reads averages out to the dose you'd like.
Be careful and weigh the gel and the dosed out gel as many times as possible!