The package was shipped and arrived promptly from Germany. Good.I tested the weights 1g to 1000g on 4 different calibrated balances (read-out fineness 0.1 mg to 10 mg) to look for any deviation from stated weight.First conclusion: The weights are at least class F2 and may well be class F1. I ordered another weight set and will follow-up on this review. Thus, I give for now 4 stars, and if I can prove that it is class F1 I will give 5 stars.The weights are made of stainless steel.I must note that the weights 100g to 1000g have a screw-cap in the bottom with a calibration chamber and a loose piece inside. The manufacturer uses this to adjust the weight exactly. (The description seemed to indicate that these weights would not have such a chamber - but, they have.) I just hope that it will not corrode over the years to come leading to a drift in weight. Time (years) will tell. If all pieces are stainless steel and the weights are kept in a dry place in the box then I guess not.Note: I did not yet test the weights in the range below 1g. This will be done when I have the 2nd box.Continued Feb 2021: Now I have my 2nd set (arrived promptly as well) and I started to check. The quality is the same as the first set - at least class F2.It turns-out that checking if it is class F1 requires an extremely good balance, e.g. for the 1 kg weight the maximum deviation from true 1000 g is 5 mg. With my balance I can say that the two 1 kg weights weigh exactly the same within +- 5 mg on each. Both give a read-out of 999.97g on my balance thus a difference less than 0.01g = 10 mg = +- 5 mg on each. The 30 mg difference from 999.97 g to 1000.00 g is likely due to an imperfect calibration of my balance. For the two 500g weights the read-out is 499.994 and the difference is thus less than 0.001g = 1 mg = +- 0.5 mg on each (up to 2.5 mg is acceptable for F1). For the 200g, 100g, and 50g weights the difference between the weights in each set is 1 mg or less. I would say that it looks convincing as F1.I briefly checked the weights below 50g. They seem all spot-on within 1 mg. Also, below 1g looks spot-on within 1 mg. I did not test below 50 mg.Now, this was mainly comparing the weights among themselves - and here they are F1. But, how about absolute deviation from the true stated weight? (e.g. what if the manufacturer makes perfect weights with high precision - but, his balance has an error giving all his weights an error from the true stated weight?). To test this, one would need a perfectly calibrated 0.1mg balance. But, I realized in this work - using 4 different professional mg and 0.1 mg calibrated (!) balances - that this is very hard to find: All showed somewhat different read-outs on the last digit (0.1mg, 1 mg, and 10 mg). So, I can only make a best estimate: Looking at all my measurements on all the balances I get the stated weight within 1 mg for all weights 100 g to 100 mg. For 200 g to 1 kg the values still indicate F1 or very close.Interestingly: With these we
Alberto 
