Those that have a decent milligram scale you can push a button called TARE. You can put whatever you want on the scale and when you push it, it zeros it out, so when you put the product on, you are getting just the weight of whatever the product is. It isn't rocket science. I use it all the time. So, all you would have to do is but the bag on the scale, push TARE then fill up the baggie and then you have the correct weight of the product.. Its a great feature. even the cheap ones should have this feature...