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This page describes an obsolete unit.

The unit described on this page was in use prior to modern methods of precision measurement. It was based on a standard which is no longer available, and which is not capable of being calibrated against modern measurement units. Therefore, the equivalence to modern SI units or to current United States customary units can only be considered approximate.



The Pound

The Tower Pound

The system called tower weight was the more general name for King Offa's pound. This dates to 757 AD and was based on the silver penny. This in turn was struck over Arabic dirhams (2d). The pound was based on the weight of 120 Arabic silver dirhams, which have been found in Offa's Dyke. The same coin weight was used throughout the Hanseatic League.

The mercantile pound (1304) of 6750 troy grains, or 9600 tower grains, derives from this pound, as 25 shilling-weights or 15 tower ounces, for general commercial use. Multiple pounds based on the same ounce were quite common. In much of Europe, the apothecaries' and commercial pounds were different numbers of the same ounce.

The tower system was referenced to a standard prototype found in the Tower of London and ran concurrently with the avoirdupois and troy systems, until it fell out of use and was abolished in 1527.

The tower pound is equivalent to about 350 grams.[1][2]

Relationship between London and tower weightsEdit

1 London pound = 1⅓ tower pounds = 7,200 troy grains
¾ London pound = 1 tower pound = 5,400 troy grains
1 London ounce = 1 tower ounce = 450 troy grains
1 London pennyweight = 1 tower pennyweight = 22½ troy grains

Relationship between merchants' and tower weightsEdit

1 mercantile pound (15 oz) = 9,600 tower grains = 6,750 troy grains
1 tower pound (12 oz) = 7,680 tower grains = 5,400 troy grains
1 tower ounce (20 dwt) = 640 tower grains = 450 troy grains
1 tower pennyweight (dwt) = 32 tower grains = 22½ troy grains

Comparison of different English pounds

English pounds
Unit Pounds Ounces Grains Metric
metric Lond. avdp. merc. troy tower troy tower avdp. troy tower g kg
Metric 1 15/14 11/10 8/7 4/3 10/7 ≈ 16 ≈ 171/7 ≈ 173/5 ≈ 7716 ≈ 10974 500 1/2
London 14/15 1 36/35 16/15 5/4 4/3 15 16 1616/35 7200 10240 ≈ 467 7/15
Avoirdupois 10/11 35/36 1 28/27 175/144 35/27 147/12 155/9 16 7000 99555/9 ≈ 454 9/20
Merchant 7/8 15/16 27/28 1 75/64 5/4 141/16 15 153/7 6750 9600 ≈ 437 7/16
Troy 3/4 4/5 144/175 64/75 1 16/15 12 124/5 1329/175 5760 8192 ≈ 373 3/8
Tower 7/10 3/4 27/35 4/5 15/16 1 111/4 12 1212/35 5400 7680 ≈ 350 7/20


ReferencesEdit

  1. "Weights used for gold". Tax Free Gold. http://www.taxfreegold.co.uk/weights.html. Retrieved 2011-01-14. 
  2. "A brief history of the pound". The Dozenal Society of Great Britain. http://www.dozenalsociety.org.uk/history/poundhist.html. Retrieved 2011-01-14. 

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