The definitions of other units that doesn't depend on the kilogram are somehow constants, like the speed of light, the second, the meter (defined with respect to the previous 2) and so on. However when it comes to the kilogram, we're still using a definition of 1889. It's definied as the mass of an alloy prototype kept near Paris. Of course its mass changes over time and so does our definition of kilogram, which is (or should be) unacceptable IMO, nowadays. Why are scientists waiting for so long to change the definition to something like "1 kilogram is the mass of 250/3 moles of carbon 12"? If you say that the mass of the prototype doesn't change noticeably, then why did we even bother to "fix" the speed of light and also get such an accurate definition for the second? The definition of the kilogram influences the definition of the coulomb, the ampere, the joule and thus, I'm guessing, the electron volt. P.S.:I had posted a similar post over 1 year ago and the thread got deleted after 1 day. I don't think it was an admin work (they would have locked the thread if it had went bad, which I don't think it had), more likely like a database error, hence I "repost it".