Hello, I happen to work in the measurement business more or like and I could read what they have to say about what is 1 kg, it is related to the Bureau des poids et mesures, the people that makes the standard about weights. Well, what can I say, the work they do is quite serious and they know what they are doing with what is an 'error' of measurement. And this is just ordinary weights, the standards they use is of a very high level, You can search on the internet about it and you will see that this notion of error is not as naively wrong as you may suggest. Now, the CODATA measurement process and the error they claim to have, I do not think that they are wrong about that, this is perhaps 2 layers higher from what I can see here at the ordinary level. I think they know perfectly what is an error. So in my humble opinion : think twice, they are probably right about the error. Best regards, Simon Plouffe