Cryogenics scale, both of which measure from absolute zero, rather than more usual scales such as Celsius or Fahrenheit, with their zeroes at arbitrary temperatures. The word "cryogenics" stems from Greek "κρύο (cryo)" – "cold" + "γονική (genic)" – "having to do with production". Cryogenic fluids with their boiling point in Kelvin Liquefied gases, such as liquid nitrogen and liquid helium, are used in many cryogenic applications. Liquid nitrogen is the most commonly used element in cryogenics and is legally purchasable around the world. Liquid helium is also commonly used and allows for the lowest attainable temperatures to be reached. These
Numeral prefix words with the same spellings (such as and ). Several technical numerical prefixes are not derived from words for numbers. ( is not derived from a number word, for example.) Similarly, some are only derived from words for numbers inasmuch as they are word play. ( is word play on , for example. See its etymology for details.) The root language of a numerical prefix need not be related to the root language of the word that it prefixes. Some words comprising numerical prefixes are hybrid words. In certain classes of systematic names, there are a few other exceptions to