The difference is 25 or 50 micrograms. It’s muuuch heavier than a virus.
The milligram weigh sets (1 milligram = 1000 microgram) are/were standard equipment in a chemistry lab (Now, if you are lucky, you get an electronic balance.) The smaller weights are only a small tin of 1 milligram. See the images in the middle of this page: http://www.ebay.com/itm/STAINLESS-STEEL-MILLIGRAM-WEIGHT-SET...
I found a microgram weight set in Internet. (But I haven’t seen any of them in real life) http://cn.mt.com/cn/zh/home/products/Laboratory_Weighing_Sol... . These weights are only a small piece of thin wire, and you must handle them with a special tool because the fingers are too dirty. The smaller weight is 50 micrograms, that is approximately the variation between the kilo prototypes.
The milligram weigh sets (1 milligram = 1000 microgram) are/were standard equipment in a chemistry lab (Now, if you are lucky, you get an electronic balance.) The smaller weights are only a small tin of 1 milligram. See the images in the middle of this page: http://www.ebay.com/itm/STAINLESS-STEEL-MILLIGRAM-WEIGHT-SET...
I found a microgram weight set in Internet. (But I haven’t seen any of them in real life) http://cn.mt.com/cn/zh/home/products/Laboratory_Weighing_Sol... . These weights are only a small piece of thin wire, and you must handle them with a special tool because the fingers are too dirty. The smaller weight is 50 micrograms, that is approximately the variation between the kilo prototypes.