Just thought this was important to those who can't afford a very expensive scale.
With my own milligram scale, it keeps on wanting to go back to zero if it's close to zero.
So I turn my scale on without the tray. Then I put the tray on and I don't tare it. I write down the weight shown (2.500).
Then I can put about 10mg on and it shows 2.510.
I then calculate the difference (10).
Seems to be +/-1-2mg on the cheap $20 Gemini from eBay.