The first scale to be created, the Fahrenheit scale, was created by Gabriel Fahrenheit (a German physicist and the inventor of the mercury thermometer) in 1724. In inventing his thermometer, Fahrenheit had to develop a scale to measure temperature. He used temperatures that he thought would be easily reproducible to define 0 and 100 degrees. 0 was set at the lowest temperature that he could obtain with a slurry of ice, water, and salt. 100 was set at the body temperature of one of his lab assistants. (The assistant was slightly feverish that day.) It also turned out that human body temperature is not constant. If varies significantly over the course of the day and from one person to another. So, while the value of 0 was reproducible, the value for 100 was not. So, enter Anders Celsius, a swedish astronomer, who proposed the centigrade scale in 1742. He proposed a scale that set 0 at the melting point of pure water and 100 at the boiling point of water at sea level. These are much easier values to reproduce. So, throughout the scientific community and much of the world, this is the scale that is favored. One thing to keep in mind about temperature, is that it is a measure of the amount energy (heat) contained by a substance. With both the Fahrenheit and Celsius scales 0 does not represent the coldest possible temperature, the point at which a substance contains no heat. This is a value of known as absolute zero and was first calculated by William Thomson, 1st Baron Kelvin. His scale starts with absolute zero as the 0 value. Many of the equations that involve temperature will only work if you use temperatures on the Kelvin scale. FYI, there is actually a fourth temperature scale. The Kelvin scale uses the same temperature increment as the Celsius scale. (That is the change in temperature between 272 K and 273 is the same as the difference between 0 degrees C and 1 degree C). The fourth temperature scale also uses absolute zero as a starting point, but it uses the temperature increment of the Fahrenheit scale. However, this scale is not used very much and I can't even remember what it is called.