I think you should keep a couple things in mind when using a scale that only reads x.xx
To start, .02 does NOT mean its 20mg. Assuming no +/- tolerances, .02 would probably mean .016-.024 mg.
Seeing as there is a +/- tolerance involved with scales, you are probably at best ending up with a range of approx 10 to 30mg.
You get what you pay for.
I highly recommend that anyone looking for a mg scale, actually start with a scale that claims to be a mg scale, ie. should be accurate to 3 decimal places to the right of the decimal point (x.xxx).
There would also be a tolerance, especially at such small amounts, but would for sure get you closer than using a scale that only reads in hundreths........
Also, most inexpensive scales will not be extremely accurate at such small weights...........
Just saying...............