With division of labour, the produce of one's own labour can fill only a small part of one's needs. Different commodities have served as a common medium of exchange, but all nations have finally settled on metals, which are durable and divisible, for this purpose. Before coinage, people had to weigh and assay with each exchange, or risk "the grossest frauds and impositions." Thus nations began stamping metal, on one side only, to ascertain purity, or on all sides, to stipulate purity and amount. The quantity of real metal in coins has diminished, due to the "avarice and injustice of princes and sovereign states," enabling them to pay their debts in appearance only, and to the defraudment of creditors. Of the Wages of Labour: In this section, Smith describes how the wages of labour are dictated primarily by the competition among labourers and masters. When labourers bid against one another for limited opportunities for employment, the wages of labour collectively fall, whereas when employers compete against one another for limited supplies of labour, the wages of labour collectively rise. However, this process of competition is often circumvented by combinations among labourers and among masters. When labourers combine and no longer bid against one another, their wages rise, whereas when masters combine, wages fall. In Smith's day, organised labour was dealt with very harshly by the law. Smith himself wrote about the "severity" of such laws against worker actions, and made a point to contrast the "clamour" of the "masters" against workers associations, while associations and collusions of the masters "are never heard by the people" though such actions are "always" and "everywhere" taking place: "We rarely hear, it has been said, of the combinations of masters, though frequently of those of workmen. But whoever imagines, upon this account, that masters rarely combine, is as ignorant of the world as of the subject. Masters are always and everywhere in a sort of tacit, but constant and uniform, combination, not to raise the wages of labour above their actual rate [...] Masters, too, sometimes enter into particular combinations to sink the wages of labour even below this rate. These are always conducted with the utmost silence and secrecy till the moment of execution; and when the workmen yield, as they sometimes do without resistance, though severely felt by them, they are never heard of by other people". In contrast, when workers combine,