MEASUREMENTS HISTORY!  

Units of weight have been around since people started to trade with each other thousands of years ago. Different civilizations created many different systems of weighing, with standards usually enforced by their rulers. Many ancient scales for weighing heavy items would have used stones, and the “Stone” is used today as a unit in some places, for example in England, for measuring the weight of a person (1 Stone = 14 pounds = 6.35 kg).

Pounds and Ounces
Many civilizations used locally common edible seeds such as corn or wheat as the basis of standard weights. In England, the “Grain” was the weight of a one grain seed from the middle of an ear of barley. The Romans used the “Pondo” (Pound), a weight defined variously between 4944 and 5220 grains. The “Pound” was also used for money, so to differentiate they referred to the “libra pondo”, Latin for “pounds weight”. This is the origin of the abbreviation “lb”. The Romans subdivided the Pound into 12 unciae (Latin for 1/12th parts), the origin of the word Ounce (and also of the word "Inch"). After the Romans left England in 449 AD, the “Pound” continued to be used. The “Tower Pound”, kept in the Tower of London, weighed 5400 grains. This defined the standard until 1527, when Henry VIII replaced it with the Troy Pound, weighing 5760 grains, named after the French city of Troyes. By this time, most goods traded across the sea between England and France were weighed using ounces of a similar weight to those in common use, but the pound was the 7000 grain “Avoirdupois Pound” (from the French, meaning “to have weight”, which was subdivided into 16 ounces, This 16 ounce Pound was soon more widely adopted, with standard English weights kept in the Houses of Parliament in London. Several other countries, including the USA, have created and used their own standards. On July 1, 1959, all English speaking countries agreed to adopt a common standard Avoidupois Pound weighing exactly 453.59237g.

In many countries that today use the metric system, people use “pound” as an unofficial term for half a kilogram (500g), for example the German “Pfund”, the Dutch “Pond” and the French “Livre” (from the Latin libra pondo).

Tons
The word “Ton” derives from the English "Tun", a large heavy barrel used to store wine or beer. One Ton was the weight of a full Tun. Today, a Tun is 210 Imperial Gallons (252 US Gallons). A US ton is 2000 pounds (907.185 kilograms). A British (Imperial) ton is 2240 pounds.

Newtons (weight and mass)
The English scientist Isaac Newton (1642-1727) recognized the difference between weight and mass. Weight is a force. All bodies have mass; a force (e.g. gravity) is needed for them to have weight. A Pound, Stone or Kilogram “standard” would weigh much less on the moon and nothing in space. Similarly, our “weight” reduces if we are accelerating down in an elevator. Pounds, Ounces, Kilograms etc. are therefore, strictly speaking, units of mass, not weight.

The Newton (N) is a true unit of weight. It is defined as the amount of force required to accelerate a 1 kg mass at a rate of one metre per second per second. A 1 kg mass near the Earth's surface has a weight of approximately 9.81 N. Gravity varies around the Earth and with height above sea level, so the weight of a 1 kg mass varies by a few tenths of one per cent depending on where it is on the Earth's surface. The Newton was first used around 1904 and was officially adopted by world scientists in 1948.

The metric system
In 1790 the French adopted a completely new measuring system developed by their Academy of Science. The word, “metre,” comes from the Latin word “metrum”, meaning “measure.” Rather than grains and stones, the metric system was based on what were considered to be constant natural quantities and used decimal (units of 10) multiples and divisions. The metre was defined as one ten-millionth part of the distance from the Earth's pole to the equator. The kilogram (kg) was defined as the mass of one cubic decimetre of water at a temperature of 4°C. A gram (g) is the mass of one cubic centimetre of water at 4°C. Many countries started to adopt the kilogram, and many made their own standard metal weights, but these were all slightly different. In 1875, representatives from many counties attended the Convention du Mètre, held in Paris, where they agreed one international standard.