Troy weight them Holland troy, Paris troy, etc. Their values varied from one another by up to several percentage points. Troy weights were first used in England in the 15th century, and were made official for gold and silver in 1527. The British Imperial system of weights and measures (also known as Imperial units) was established in 1824, prior to which the troy weight system was a subset of pre-Imperial English units. The troy ounce in use today is essentially the same as the British Imperial troy ounce (1824–1971), adopted as an official weight standard for United States coinage by Act of
Heavy metals or in balance weights on wheels and crankshafts, gyroscopes, and propellers, and centrifugal clutches, in situations requiring maximum weight in minimum space (for example in watch movements). In military ordnance, tungsten or uranium is used in armour plating and armour piercing projectiles, as well as in nuclear weapons to increase efficiency (by reflecting neutrons and momentarily delaying the expansion of reacting materials). In the 1970s, tantalum was found to be more effective than copper in shaped charge and explosively formed anti-armour weapons on account of its higher density, allowing greater force concentration, and better deformability. Less-toxic heavy metals, such as