I often wonder why they don't make a set of scales with a electro magnet at one end that attracts one end of a balance and you place the weight on the other end

I often wonder why they don't make a set of scales with a electro magnet at one end that attracts one end of a balance and you place the weight on the other end and adjust the strength of the magnet until you get a balance and from there can measure out that same weight. Now would need very well pression made electro magnet and balance. Though idealy the ability to measure out a fixed amout of atoms of element and wheigh that and work out the relationship of how many atoms of element X is needed for a kilo. Well until then it is one of the last area's of measurment that history still firmly has its teeth into. Was nice TV show in the UK not long ago that covered the whole area of weights and measures from the science and history of them comming about. One of the better science shows. http://www.bbc.co.uk/programmes/b02xgf5d http://www.bbc.co.uk/programmes/b02xgf5d "Deep underground in a vault beneath Paris lives the most important lump of metal in the world - Le Grand K. Created in the 19th century, it's the world's master kilogramme, the weight on which every other weight is based. But there is a problem with Le Grand K - it is losing weight. Professor Marcus du Sautoy explores the history of this strange object and the astonishing modern day race to replace it."