Imperial and US customary measurement systems different concepts – the imperial gallon is defined in terms of the volume occupied by a specified mass of water, while the US gallon is specified in terms of cubic linear measure. Notes Notes Units of weight in both the imperial and US customary system always used the same standard, though differences in multiples of the avoirdupois pound developed in the nineteenth century. Both systems used the three different scales – the avoirdupois system for general use, the troy system for precious metals and the apothecaries system in the pharmacy industry. The term "weight" and "mass" are used interchangeably in
Heavy metals for the manufacture of artefacts such as tools, machinery, appliances, utensils, pipes, railroad tracks, buildings and bridges, automobiles, locks, furniture, ships, planes, coinage and jewellery. They are also used as alloying additives for enhancing the properties of other metals. Of the two dozen elements that have been used in the world's monetised coinage only two, carbon and aluminium, are not heavy metals. Gold, silver, and platinum are used in jewellery as are (for example) nickel, copper, indium, and cobalt in coloured gold. Low-cost jewellery and children's toys may be made, to a significant degree, of heavy metals such as chromium,