Balances had been constructed long before the theory of levers was completely understood. The balance with a pointer on arms of equal length and weights (instruments 14 to 16) comes from ancient times. From the third century BC it competed with the "Roman" balance which had a sliding pointer on a graduated shaft (instruments 18 and 19). The two kinds are known as drop-pan balances since the pans are below the pointer. It was Gilles Personne de Roberval who, in 1669, devised a balance with raised pans, kept horizontal by an articulated parallelogram. It was not until the 19th century, however, that Roberval's balance became widely used in shops and homes.
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